A quick, simple guide to MY succubi (and inccubi)
They have four primary skin colors, and a sort of 'ranking system' that goes with it, it's not like there are slaves or anything. Actually, all succubi are treated like royalty in the Underworld.
It's just that some skin colors are rarer than others, and if a succubi has said skin color, then they're a SPECIAL SNOWFLAKE.
In a particular bloodline/family of succubi, the primary skin colors always stay the same, with change in tone obviously. They're numbered from rare to common, 1 being the rarest, which is pitch black to light gray.

Legs/feet and tails are another difference. But, unlike skin color, they can change within families. For example, Morgan has goat feet/legs and a spearhead tail, whereas Kalzfir has reptilian feet/legs and a spearhead tail.