Red-green was in the context of mixing colors, not color-blindness here. If you e.g. mix oil/tempera colors, red and green give you a really ugly grey color; on the edges between red and green patches you'd get something similar.

I have the opposite issue - my color perception is 100%, so I can distinguish very slight differences in color tones. What might look acceptable to you might be unacceptable to me and vice versa ;-)