I was surprised when I first learned that color blindness doesn't actually mean you can't see certain colors. Color blind people might see the colors very differently or very similarly depending on their condition. Vischeck is a website that has some interesting information as well as clear examples on the variations of color blindness. They also have a special page that applies an algorithm to images to help people with color blindness to "see" the colors they're missing.
All of this reminds me of the first time I'd encountered someone with color blindness. I was in my early 20's and had gone into business with a friend of mine. One part of our shop was devoted to t-shirts with customized artwork and slogans that could be ironed on to order. Greg was the tall, funny kid who lived across the street from my house and we'd hired him to be our delivery driver. But after days of pestering us to work the front counter, we finally relented and let him work up front one morning when he didn't have any deliveries. About five minutes later, Greg comes running back to my desk in the back, whispering, "Hey Robert -- Could you help me out up front with a customer?"
As we headed up to the counter, I asked him, "What's the problem? This guy giving you a hard time, Greg?" To which he muttered back, "I'm colorblind. I can't tell which t-shirts are red!" After helping him take care of the customer, I think we all ended up spending an hour or two asking him all sorts of questions about his condition; when did he first find out, what's it like, what does he see... Being artists, my partner and I were completely fascinated. Oh -- and we ended up tagging the shelves of t-shirts so that the colors were marked on labels so Greg could help out at the front counter.
In the end, do we really know who actually sees normally and who sees differently?