I'm color blind and know the frustration to not be able to play some videogames or read charts which use very similar colors (at least to me).
A lot of people don't even understand what color blind really is, it's a funny thing to explain what it is and joke about it with new friends / coworkers when the subject comes along.
At least my coworkers now ask me first when choosing color coded post-it for the current project ;).
Too true. Two otherwise sensible, college-educated friends of mine once insisted that they'd be able to tell how my eyesight is different if I sat down and drew what I see out of the window. Using pencil crayons that presumably pierced through my colourblindness. I literally could not find a way to explain to them why it made no sense.
"No, but we'll cover up the writing on the pencils so you can't read what colour they are"
EDIT: I realise I misrepresented the scenario. This wasn't talking about colour-blindness specifically, but in more of a "maybe the blue you see is my red" scenario.
Suppose you were red-green colorblind, and there was an apple tree with green "Granny Smith" apples outside your window. You can't tell if the leaves on the tree are red or green, but using common sense, you guess that they are green, and color them with the green pencil. You can't tell if the apples are red or green, but using common sense, you guess that they are red, and color them with the red pencil. "Ah ha", says your friend, "you colored the apples with red when they are actually green. You must be red-green colorblind"
When I was in kindergarten, the teacher gave us the assignment of drawing a brown bear. Mine was green.
In my experience doing an Ishihara test (http://en.wikipedia.org/wiki/Color_perception_test) whith someone else while telling them what are you seeing on each pod does wonders to make them understand specifically what shades of color cause you troubles, that's how my wife got to understand my color blindess.