Colorblindness affects about 2% of men and .5% of women in one form or another. When you're colorblind, you miss out on a lot of things happening in the color spectrum like stoplights. Although it's not the worst disease or condition a person could have, it is a common affliction, and many people who can see the full color spectrum aren't aware what colorblindness can do to a person.
This list of stuff you're missing if you're colorblind is a test of sorts: If you can see all the images on the colorblindness test, be grateful for your color recognition skills - and be aware of the frustration colorblind people might feel. If you can't see the colorblind images, and aren't already aware you are colorblind, you can find tips for what to do from the Colorblind Association.