Do you want to simulate a color blind vision? Go to Vischeck and try it online. You can find out what an image or a webpage looks like if you suffer from Deuteranope, Protanope or Tritanope. I think this tool is just great and for me I often can’t see any difference between the original image or the simulated images neither for Deuteranope nor for Protanope. On their webpage you can even find a PhotoShop plugin to download for free. The plugin offers the same image corrections as described above.
A second but for us color blind people even more interesting tool is the online Daltonize of images. Daltonize tries to correct images for color blind people. You can adjust a red/green stretch factor (Deuteranope and Protanope), a luminance correction and a blue/yellow correction (Tritanope). Give it a try and see what you maybe can’t see yet.