If you're red-deficient, then purple/blue is also a bad choice for colors because you can't see the red components of purple.

Blue and purple are the same color as far as I can tell.

Red/blue would be safer colors to differentiate for many colorblind people. Red/green colorblindness is so common it baffles me that comparisons using red/green are still so prevalent. Especially considering how heavily biased the tech population is toward men.

And as Sanddancer points out, any colors that make use of red/green are going to be problems as well. (hence blue/purple being an issue as the difference is the red component).

In a given group of 5 men, you have a 50% chance that 1 is red/green color deficient.

> In a given group of 5 men, you have a 50% chance that 1 is red/green color deficient.

Soooo, 1 in 10 men are red/green colour deficient?

I believe that implies 1 in 8 people are.

    Pc = Probability that someone is colorblind
    (1 - Pc) = Probability they aren't colorblind
    (1 - Pc)^5 = Probability that no one in group of 5 is colorblind
    1 - (1 - Pc)^5 = Probability that someone in group of 5 is colorblind

Solve .5 = 1 - (1 - Pc^5): http://www.wolframalpha.com/input/?i=.5+%3D+1+-+%281+-+p%29%...

You get .129449, which is approximately 1 in 8

Although wikipedia shows 7% of males, meaning a group of 5 would have a 30% chance of one of them being colorblind.

I will let others dissect the different probabilities for at least 1 and for only 1 and say, yes! Nearly one in ten: http://www.colour-blindness.com/general/prevalence/

It usually doesn't come up in conversation. Even when I was working on an image processing toolkit, it was several months before I realized my boss was red-green colorblind.

I'm red/green colorblind and blue/purple is the worst combination for me. I colored all my skies purple in elementary school because I couldn't tell the difference.

Purple is blue+red, so my son who has a very common color deficiency can't tell purple from blue at all. They look completely the same to him.