Color idioms in multiple languages, including German
There is this interesting project by Alan S. Kennedy to collect as many of the well-known color idioms of languages: http://www.starchamber.com/colors/color-idioms.html.
I've never heard black on white, just "it's in black and white" or "it's/...is black and white". Different meanings for those two. First means the answer/result/etc. is clear and straightforward, and the second means the difference between two things is obvious.