You can't subtractively mix all colors from three practical 'primaries'
If you mix Cadmium Yellow and Ultramarine Blue you get something yucky and greyish. With Hansa Yellow and Cerulean Blue on the other hand you can get a good green but that blue won't make a good violet when mixed with Cadmium Red Light.
The color mixing rules taught in elementary school don't really work and you need roughly 12 primaries to mix any arbitrary color.
https://www.goodreads.com/book/show/2103727.Blue_and_Yellow_...
You can't subtractively mix all colors from three practical 'primaries'
If you mix Cadmium Yellow and Ultramarine Blue you get something yucky and greyish. With Hansa Yellow and Cerulean Blue on the other hand you can get a good green but that blue won't make a good violet when mixed with Cadmium Red Light.
The color mixing rules taught in elementary school don't really work and you need roughly 12 primaries to mix any arbitrary color.