I know not to wear two blue denim pieces at the same time, but I am curious if this applies to if the second piece is white. Also, what id the second piece is grey, or black/black?

The main reason I am asking this is that I am on a hunt for a couple of waistcoats to wear over graphic tees, and have been finding quite a few cute denim ones. So I am wondering if denim vest + arty tee could work with white skinnies/clamdiggers, as well as grey/black ones? Or should I just stick to non-denim vests?