For me, the primary meaning of "colour" is basic color term
and a "shade" is a lighter or darker variation of one of those basic colours. So pink isn't a "shade" of red to me, even though a mixture of say, blue and white or green and white would be.
Now, since grey represents an admixture of white and black, where you draw the line between a "shade of black" and a "shade of grey" is pretty arbitrary. For me, it would probably vary according to context--not just the speech situation, but also, say, what other colours it was next to or whether we were talking about the colour of a piece of cloth or a dog or a patch of sky.
"Richmond is a real scholar; Owen just learns languages because he can't bear not to know what other people are saying."--Margaret Lattimore on her two sons