The chalk is what you use in school to write on a blackboard, which is, as you know, glaring white.
It would have been easier to make sense of if it had had the hyphen - chalk-white; that makes it clear that "turn" means "become".
Without the hyphen, I understood "turn" in the sense of "transform". In that sense, to turn chalk white would make sense if the chalk was red to start with!
Meaning of 'turn chalk white' 
It would have been easier to make sense of if it had had the hyphen - chalk-white; that makes it clear that "turn" means "become".
Linear Mode
