They are almost impossible to tell apart in a lit sky.

When the sky is dark, red stars are very distinctive, I don't think even color blind people would have a problem. (I am color blind, but I confuse blue and green, not red and green.)

Both yellow and blue stars emit blueish and yellowish light, and are much harder to tell apart.

As an added bonus, red stars are the first to disappear against a lit sky :(