So, if the black coloration that all Kuros have is a result of Darkness, is it possible that their scales can be different colors beneath it?

Everything about a Kuros is Darkness, from spiritual, abilities, and body. They can have secondary colors, buuuut the only way they can have all colored scales is either by illusion, or they’re hybrids. Removing Darkness from a pureblood Kuros would probably kill them unfortunately D: 

Unless I got the question wrong I’m sorries if I misunderstood it 8,D There are different scale types for Kuros (Something I plan on getting into more too). A lot of them have ‘thin scales’, like Feuriah, which are more like snake/lizard skin, while others like the Brokt and Allus can have thick layers of scales that offer better armored protection. Though usually, the ‘skin’ is still black/grey, or whatever secondary colors.

~Weird Hyenas