Not quite sure what you are asking but the Tint colour uses two hex numbers for each of red green blue from 0 to FF or 255. So it uses format RRGGBB.
It is a tint, meaning it acts like a shading of the existing colors that are already on the icon.
FFFFFF I think will change absolutely nothing since this colour is pure white and white plus any other colour just gives the same colour again. Likewise, 000000 will just give you everything solid black.
Yeah I was looking at some unity stuff and all I could find was Albedo. I have a hacky thing that comes close to doing what I need. Just a basic visually similar previewer.