The original reply is actually correct. From Wikipedia: "For a subtractive combination of colors, as in mixing of pigments or dyes, such as in printing, the primaries normally used are magenta, yellow, and cyan,[1] though the set of red, yellow, and blue is popular among artists."

I also learned the RYB colors as primary colors, and find it much easier to reason about than CMY. That's probably also the reason why artists use it.

For the 'simple' language, I agree that RYB + white and black are enough.