You need to understand the nature and science of color to know you can't make a black turn to white. (or a Pig's ear into a Silk Purse.
One thing to understand is that "clear" is not the same as "white" . The terms White, Gray and Black refer to pigmented materials. The other colors can be applied to clear(use a dye for the color) or pigmented materials.
Black absorbs all frequency's of light whereas White reflects all frequency's. Even over molding of a black with a white often does not work as the black substrate affects the white overcoat. Have you ever tried to cover a Black paint with a white paint? It usually takes several coats to cover the black.
Optical brighteners will make the color richer in that they convert non-visible frequencies into visible ones.
There are a number of reference books on color as well as the use and principals of colorants. Recomend you check one out from your nearest technical library if not actually buying one.
"If you want to soar with the Eagles in the morning.......
You can't hoot with us Owls all night"