Colorblind Colors of Confusion

When people hear that you are red-green colorblind, most of them think, that you can not distinguish between red and green. But that is wrong.

Of course, red and green are some of the problem colors when you are suffering from red-green color blindness. But…

  • … some shades of red and green are easily to distinguish,
  • … and many other colors also cause problems.

The following diagrams of the CIE 1931 color space can give you a quite good understanding of which colors are problematic for colorblind people.

Protan Lines

Deutan Lines

Tritan Lines

All colors in the direction of the lines might be hard to differentiate. There are three different diagrams corresponding to the three main color vision deficiencies: protanopia (red-blindness), deuteranopia (green-blindness), and tritanopia (blue-blindness).

Copunctal Point x y
Protan 0.747 0.253
Deutan 1.080 -0.800
Tritan 0.171 0.000

See Wyszecki & Stiles, Color Science (2nd ed.), 1982, Table 1 (5.14.2) p. 464

The lines shown above are called confusion lines and converge at a point which is called the copunctal point. For the three different types of color vision deficiency there are three different copunctal points.

For the two types of red-green color blindness (protanopia and deuteranopia) the main problem area of colors is really in the axis between red and green. And on this side of the color space, the confusion lines are quite the same for both types. This is why they are called red-green color vision deficiency. But on the left side of the diagram you can see that they are quite different confusion lines which show the problem colors.

If you would like to learn more about color matching and confusion lines you might like to read the article Color Matching and Color Discrimination by Joel Pokorny, a very well known researcher in the field of color vision deficiency.

As you can see from the above diagrams, the whole spectrum of colors is some way reduced for colorblind people. It is definitely not only red and green (protanopia/deuteranopia) or blue and yellow (tritanopia) which can not be distinguished.

Photoshop CS4 Accessibility Enhancement Incorporating Color Blindness

Photoshop CS4
Photoshop CS4

If you are designing graphics for a web page you have to keep in mind to make them also accessible to colorblind persons.

With Photoshop CS4 Adobe introduces soft proofing for color blindness, a great support just for this task.

The new soft proofing filters for color vision deficiency were developed in corporation with the Japanese Color Universal Design, a user-oriented design system, which has been developed in consideration of people with various types of color vision, to allow information to be accurately conveyed to as many individuals as possible.

Adobe Photoshop CS4 supports the following two color blindness filters, which combine the two most common forms of color vision deficiency:

Photoshop CS4 Color Blindness Option
Soft Proofing on Color Blindness

To determine whether your document is CUD-compliant or not, step through the following three simple steps:

  1. Convert the document to RGB color mode, which provides the most accurate soft proofs for color blindness.
  2. To simultaneously view the original document and a soft proof, choose Window > Arrange > New Window (optional).
  3. Choose View > Proof Setup > Color Blindness, and then choose either Protanopia-type or Deuteranopia-type.

To comply with CUD, you have to check your document in both views.

If you are a graphic/web designer, don’t forget to check your graphics on accessibility for colorblind users. Photoshop CS4 is one of the tool which can help you to fulfill this task—the color blindness simulator Coblis another (online) one. You might find some other helpful tools on my list of 15 Tools If You Are (Not) Colorblind.

Thanks to Jay Kinghorn and his article on Photoshop CS4: Color Blindness Proofing. You can also find more information on color blindness validation at the Adobe Photoshop CS4 accessibility overview.

Color Blindness: Can Colored Contacts Help You?

Many people who either newly learn about their color blindness or who would like to get a job which requires normal color vision, are looking for a way out. As there is no cure for color vision deficiency, improving color vision with lenses for the colorblind seems to be a nice possibility.

The question arises now, can such colored contacts really help you if you are colorblind?

Colored Glasses
Possible view through colored glasses.
Photo taken by Malingering

The following discussion refers to a product called ChromaGen, most probably the best known colored contacts aiming to help colorblind people.

The ChramaGen: A practitioner report is the most often cited report about visual aids for colorblind people. Unfortunately this source seems to be very optimistic and more like some surreptitious advertising.

It is well known, that colored contacts can only alter the perceived colors but can not enhance the spectrum. For example Dr. Natalie P. Hartenbaum states very clearly that lenses don’t correct color blindness contrary to some of the vendors, which make it look like as they could cure color blindness with their products.

ChromaGen lenses
Colored contact one eye only

Unfortunately I can not tell you anything about my personal impressions as I have never tried such lenses. But I would like to cite some others who did try colored contacts in hope to find something against their color vision deficiency under certain circumstances or even in everyday life.

Faborito says the following about his ChromaGen lenses (Link):

My life has changed in a way a have no words to describe. Last year i saw red for the first time in my life. Is amazing!!!! You have no idea what is like to see a coke can or a tomato in full brilliant red. It’s spectacular. I used them every day, and for photography are great.

Tabascokid is also sharing his story about the Chromagen lenses (Link):

[…] The thing that is not explained in the brochures is that despite you suddenly having a broader range of visible colours, depth perception and contrast, it doesn’t help in actually recognising the colours. When I attempted to edit skin tones and subtle casts, I was still just as much in the dark. The primary colour looked lovely and punchy but I never really had issues with these anyway. Tones and hues were as confusing as ever. My brain still couldn’t get the differences.

Chris made the following experiences (Link):

With ChromaGen only one tinted lens is worn, this provides colour contrast but I found it distracting as I was unable to coordinate the contrasting visual data. Although I passed the Ishihara Colour Test with this system, I was still unable to name colours. The ColorView system changed the colour spectrum but at the expense of darkening the visual spectrum overall. This system was more akin to wearing sunglasses than anything else as I still was unable to identify colours confidently and still failed the colour test.

Azmole tried the two systems ChromaGen and ColorView (Link)

I did have some improvement when testing them with the Ishihara test. The opthamologist with Colorview had me go outside in daylight to use the lenses and many reds that I normally could not see came into view. I did not purchase the lenses because I was more interested in passing a color vision test and felt even with the lenses I would fail.

Now judge yourself if you wont to give colored visual aids a try to improve your color vision. But you have to know, that not one product can cure color blindness but only alter your color perception.

Read more details about colored contacts and glasses at Improving Color Vision with Lenses for the Colorblind.

15 Tools If You Are (Not) Colorblind

The following list of on- and offline tools for colorblind persons was put together by JNvB, the founder and owner of

This is an overview of available software and websites which either help and assist you if you are suffering from color blindness (Visolve, Daltap, eyePilot™) or tools that can show you how the world looks like for colorblind persons. Next to that, programs are indicated that can recognize color and can show the name and/or code (e.g. RGB).

Assistive Software for Colorblind People

Visolve by Ryobi System Solutions

Visolve Deflector
Visolve Deflector

Using a filter, Visolve allows better discrimination of colors by making colors lighter and/or darker, or increasing the saturation.

Unique is the ability to give each color a different hatch pattern, which is very useful for charts or diagrams.

The filters of Visolve:

  • Red/Green filter: red colors lighter, green colors darker
  • Blue/Yellow filter: blue colors lighter, yellow colors darker
  • Saturation filter: increases the intensity of all colors
  • Filtering: colors other than the specified color are darkened
  • Hatching: each color is hatched differently


  • Windows NT, 2000 or XP (probably works on 98 and Me)
  • Mac OS v10.4 or higher (probably also v10.2 and up)

Download: Visolve
Free for personal and non-commercial use.

Daltap by Glenn Heylen

Daltap Flash Unit
Daltap Flash Unit

Daltap has several features combined of which the flashing feature is the most useful. By flashing, it shows where a picked color is on your screen. Next to that, it can give the name of the color at the tip of mouse and it can also zoom in the area that is near the mouse.

The features of Daltap:

  • Naming feature: show the name of the color (basic and detailed)
  • Flashing feature: chosen color flashes on the screen
  • Mini zoom feature: enlarges the area around the mouse


  • Windows XP, Vista with Windows .NET Framework 2.0

Download: Daltap
Free to use.

eyePilot™ by Tenebraex

eyePilot Gray Tool
eyePilot™ Gray Tool

Several filters that allows better identification of colors by graying out all colors except the one chosen or by flashing a picked color. It can also make a color turn black by clicking on the name and it can show the name of color. On top of that, it can change the hue of colors, increasing the contrast between colors.

The filters of eyePilot™:

  • Gray filter: all colors gray but the picked color
  • Flashing filter: a chosen color flashes
  • Name filter: shows the name of the color the mouse points at
  • Hue filter: adjusts the saturation of colors


  • Windows NT, 2000 and XP
  • Mac OS v10.2 and higher

Download: eyePilot™
Fully functional trail version for 30 days. Thereafter an activation code is needed for which you have to pay $34.00.

ColorBlindExt by Onkar Rukar, Gaurav Savkar, and Tushar Pagar


This Firefox add-on offers the possibility to change websites, text and figures such that it is better readable for the colorblind. This can be done while browsing or via a menu with the following filters:

  • Red filter (for protanopia and protanomaly)
  • Green filter (for deuteranopia and deuteranomaly)
  • Blue filter (for tritanopia and tritanomaly)
  • Monochromacy


  • FireFox 2.0 or higher with Java Runtime Environment 1.5 or Java Advanced Imaging Run Time 1.1.3 or higher.

Link: ColorBlindExt

Color Blindness Simulation

Color Oracle by Bernhard Jenny and Nathaniel Vaughn Kelso

Color Oracle Deuteranopia Settings
Color Oracle Deuteranopia Settings

Places a filter over the screen to simulate colorblindness directly showing how it looks like for a colorblind person.

Color Oracle can simulate the three main types of color blindness:

  • Deuteranopia (green-blindness: most common form of color vision deficiency)
  • Protanopia (red-blindness: rare form)
  • Tritanopia (blue-blindness: very rare form)


  • Windows 2000, XP or Vista with Java 6
  • Mac OS v10.4 or higher
  • Linux with Java 6

Download: Color Oracle
Free to use.

ColorDoctor by Fujitsu


ColorDoctor not only simulates website display, it is also possible to simulate real-time display of for example moving images such as Flash by selecting the “Transparent” mode. It is possible to show the display content through four different conversion filters:

  • Grayscale
  • Protanopia
  • Deuteranopia
  • Tritanopia

The simulation result can be stored in various file formats, including BMP, JPEG, PNG, TIFF, and GIF.


  • Windows XP and Vista with Windows .NET Framework 1.1 or higher

Download: ColorDoctor
Free to use.

Sim Daltonism by Michel Fortin

Sim Daltonism
Sim Daltonism

Sim Daltonism filters in real-time the area around the mouse pointer and displays the result—as seen by a color blind person—in a floating palette.

Sim Daltonism can simulate eight types of colorblindness:

  • Monochromacy (complete)
  • Monochromacy (partial)
  • Protanomaly (red-weakness)
  • Protanopia (red-blindness)
  • Deuteranomaly (green-weakness)
  • Deuteranopia (green-blindness)
  • Tritanomaly (blue-weakness)
  • Tritanopia (blue-blindness)


  • Mac OS X 10.2.8 or higher

Download: Sim Daltonism
Free to use.

Online Color Blindness Simulation

Coblis by Colblindor

Coblis - Color Blindness Simulator

Coblis – Color Blindness Simulator

Coblis was designed to help non colorblind people to understand how an image looks like if you have a certain type of color vision deficiency.

You can either try the different types of color blindness on the given sample picture or upload your own images and see how they look if you would be colorblind.

The following types of color blindness are supported by Coblis:

  • Normal Color Vision
  • Red-Blind/Protanopia
  • Green-Blind/Deuteranopia
  • Blue-Blind/Tritanopia
  • Red-Weak/Protanomaly
  • Green-Weak/Deuteranomaly
  • Blue-Weak/Tritanomaly
  • Monochromacy/Achromatopsia
  • Blue Cone Monochromacy

Link: Coblis

Vischeck by Bob Dougherty and Alex Wade

Vischeck Daltonize Tool

The online service of Vischeck offers two types of simulation:

  • Vischeck: shows how pictures look for colorblind people
  • Daltonize: corrects images if you are colorblind

Vischeck itself can simulate the three main types of color blindness either using an image or by running it directly on a webpage:

  • Protanopia
  • Deuteranopia
  • Tritanopia

Daltonize makes it possible to adjust the ratio of red/green & blue/yellow and brightness of colors of images making them more readable for a colorblind person.

Next to the website, Vischeck offers a plug-in to do the simulations offline with the help of Adobe Photoshop or ImageJ (see Vischeck downloads):

  • VischeckPS – Windows
  • VischeckPS – Mac
  • VischeckJ 1.0

Link: Vischeck

Colorblind Web Page Filter by Matthew Wickline

Colorblind Web Page Filter Settings

The purpose of colorblind webpage filter is, as the name already suggests, to show how webpages are seen by colorblind people.

To do this, you can choose between all different kinds of color vision deficiency:

  • Monochromacy
  • Blue Cone Monochromacy
  • Protanomaly (red-weakness)
  • Protanopia (red-blindness)
  • Deuteranomaly (green-weakness)
  • Deuteranopia (green-blindness)
  • Tritanomaly (blue-weakness)
  • Tritanopia (blue-blindness)

Additionaly it is possible to toggle stylesheet inclusion, image filtering and the special case of non-gif image filtering.

Link: Colorblind Web Page Filter

Color Vision by Cal Henderson

Color Vision
Color Vision

When designing a website, brochures, etc, Color Vision comes in very handy.

On the website you pick text and background color and check how this looks like in the case of:

Trichromat: Normal
Anomalous Trichromat:   Protanomaly Deuteranomaly Tritanomaly
Dichromat: Protanopia Deutanopia Tritanopia
Monochromat: Typical Atypical

Link: Color Vision

Color Recognition

Eyedropper by



Enlarges the area around the tip of the mouse and tells which color it points to in several different color systems like HEX, RGB, and CMYK.

Next to that, it is possible to make some image capturing or use the value switchable mode, which allows you to choose between normal, grayscale and websafe colors.


  • Windows 95, 98, NT, 2000, XP, and Vista

Download: Eyedropper
Free to use.

WhatColor by Hikaru Nakahara

WhatColor Features

Enlarges the area around the tip of the mouse one to four times and tells which color it points to in several different color systems like RGB, decimal, HSV and HLS.

Additionally it gives the name of the color the mouse points to, which is very handy for colorblind users. And on top of that it can even pronounce the color names.


  • Windows 95, 98, Me, NT, 2000, XP, and Vista

Download: WhatColor
Fully functional trail version. Thereafter an activation code is needed for which you have to pay $8.00.

Online Color Recognition

Color Name & Hue by Colblindor

Color Name & Hue

Color Name & Hue

By giving in a color as a RGB, HSB, or hexadecimale colorsystem value, Color Name & Hue associates a color name and the corresponding hue out of more than 1600 colors.

Color names can also be found by placing the circle on one of the main colors followed by moving around the slider to find the hue of the color of interest.

Link: Color Name & Hue

Name that Color by Chirag Mehta

Name that Color
Name that Color

You can either select a color by its name, enter a hexadecimal color value or select a color on a color selector wheel. Name that color will find the closest match out of a list of more than 1500 colors and name it.

Link: Name that Color

Thanks very much to JNvB from for this comprehensive list of tools for colorblind and not colorblind people. If you know of any more please add them in the comments section.

Euro Coins—A Simple Color Blindness Test

Did you ever wanted to quickly make a color vision test with one of your friends? Put a few euro coins into your pocket and you will always have a simple color blindness test handy and ready to use.

Euro Coins Color Blindness Test
Euro Coins Color Blindness Test — (left) normal vision,
(center) deuteranope simulation, (right) protanope simulation

P. J. Pardo, A. L. Pérez and M. I. Suero, three researchers from the University of Extremadura, Spain, found this simple test while looking for an uncomplicated possibility to test for color vision deficiency. The discovered that there are two different classes of coins:

  • 1, 2, 5 cent coins made of copper-covered steel with a reddish tone.
  • 10, 20, 50 cent coins made of Nordic gold with a yellowish tone.

Measuring the exact colors and calculating the coordinates in the CIE color space showed, that the two different colors are arranged on the deutan confusion line. This means that green-blind people wont be able to distinguish the colors and also red-blind people will have significant problems. So they found a simple possibility to test for red-green color blindness

So this are the facts. And now, how can you perform a color vision deficiency test based on this findings?

  1. Gather 5 coins each from lower and upper values. Use coins from different countries, as they have different back sides.
  2. Mix them and show the coins with the value side facing down to your friend.
  3. Ask your friend to sort all the coins based on their colors.
  4. See how your friend performs on the task.
  5. Explain the facts why this is a valid red-green color blindness test.

Any person with normal color vision should be able to sort them quickly and of course correct. Red-green colorblind people will have more or less problems to sort them and often try to sort them based on brightness. If you try this test on several persons (including colorblind people) you will recognize the difference.

For more details on this test see Euro: A new color vision test in the pockets of three hundred million Europeans.

Happy testing! — Check the color vision abilities of your friends and your family with this simple color blindness test. It would be great to hear some of your experiences. If you like, share them in the comments.

If a Women is a Carrier of Color Blindness does she also Suffer from it?

Many people think that only men can be colorblind. As we can learn from genetics, this is not true. There are a lot more men colorblind, but also women can suffer from a color vision deficiency.

Here’s a question for experts: according to a vision test in a magazine she did recently, my mother has a slight red-green weakness, which, however, is hardly noticeable in daily life. Is this also colour blindness, although that is really rare in women, and it’s nothing compared to her father’s colour blindness, which was pretty severe? Or can it be due to her being a carrier?

On a first glance it looks like we can give a quick and short answer on this. But thinking about it, makes it a bit more complicated.

First of all, yes women can be colorblind and even if it is a very weak form of it you call it color vision deficiency (a wording which reflects much better the fact that colorblind people can also see colors). And it doesn’t matter if it is rare or not.

Sex chromosome X encodes color vision.
XY = man
XX = woman.

Now let’s have a closer look at this case. We have a colorblind man which means he has a defective X chromosome which pairs with a Y. The Y chromosomes have no coding of color vision and therefore have no important role here. His daughter will inherit this defective X and another X from her mother. We have now to possibilities:

  1. The mothers X is also defective concerning color vision.
  2. The daughter inherited an X encoding perfect color vision.

In the first case the daughter definitely shows some form of color blindness which she inherited from both of her parents. It is said that the weaker form either from her father or from her mother would control her color vision.

X-linked recessive carrier mother

According to genetics the daughter shouldn’t be colorblind in the second case. But it is known from different cases that this isn’t always so easy to tell. Up to now it is not fully understood how those two X chromosomes affect the color vision system. It could be very well that both of them play their part in the setup of the color receptors. In this case the strong color blindness encoded on her fathers X chromosome could also affect the color vision to a certain degree.

Putting this together means, that the daughter can show characteristics of color vision deficiency in the first and the second case. Only a detailed genetic analysis could tell us more details about it.

Color Blindness Simulator: New Tool Released on Colblindor

Did you ever wonder how it looks like to be colorblind? It is not easy at all to describe color blindness in words. But it is much easier to show it on an image, if you have the right tool.

Color Blindness Simulator
Color Blindness Simulator

Just today I released a second tool on Colblindor. I call it Coblis, a very effective color blindness simulator.

Coblis is based on Michael’s color matrix from ColorJack. Basically the tool manipulates the colors of an image in such a way, that the result is the same image as seen by a particular type of colorblind people.

Let’s have a look what exactly you can do with the color blindness simulator:

  • Choose from nine different color vision types.
  • All possible color vision deficiencies can be simulated.
  • Try out image manipulation with a sample image…
  • …or upload your own image to change its colors as colorblind people perceive them.

The following gallery should give you a quite good impression of what you can do with the tool. If you start with the image in the center the color blindness simulator will produce the following color blindness views (clockwise): Red-Blind/Protanopia, Green-Blind/Deuteranopia, Blue-Blind/Tritanopia, Red-Weak/Protanomaly, Green-Weak/Deuteranomaly, Blue-Weak/Tritanomaly, Monochromacy/Achromatopsia, and Blue Cone Monochromacy.

Color Blindness Simulator: Example Picture
Color Blindness Simulator: Example Picture (taken by Gaetan Lee)

If you haven’t tried it out yet, this is the time to go and check out Coblis, my color blindness simulator. Comments are very welcome.