[NegativeK]

I have the relatively typical male, minor colorblindness. Using color as an signal is fine, but just make sure there's something else that's independently conveying the info.

Also, another way to find out how common colorblindness is among your male friends: go rock climbing in a gym. Color is used on the holds to signify the route, and colorblind people who quickly start asking about color as they're climbing.