As many people have said, Colour-blindness is where you cant distinguish between certain colours such as Red/green or Yellow/Blue. A very small percent of people just see shades of gray, but that isnt common. This is a simple Colour Blindness test
Colour Blind Test [http://www.media.perthnow.com.au/multimedia/2008/04/hidden_images/colour_test.jpg].
Everybody should be able to see the first one, It is the control. The others test for the different kinds of colour blindness. If you are colour Blind, you are unable to see the number.
I would really like to know what being colour blind is like, Somehow just switch off the colour for a few. But alas....