Black Clear Crystal

Why are things that are crystal clear things said to be ‘written in black and white’?

Isn’t that being a bit mean to the other colours of the spectrum?
I kill kittens, sue me – Wow. Now you’re reaaaaaaally scaring me. I think I might have to sleep with the night-light on tonight.

yes that is mean to all the “cooler” colors in the spectrum. why cant people say “It’s written in the rainbow.”?