I was just playing around with QuickShine, added 4 drops of craft paint black mixed it and poured it over back glass, wiped off excess and this is result.
I may try it again and see if it darkens it.
It's mostly the clear parts and I QuickShine them days before but I don't want to handle them(gloves) too much.
I saw a toothpick with some sticky on it, silly putty?