The Sims 4Edit
In CASdemofullbuild.package, skintone files can be found. There are no built-in names for each colour, so herein names will be made up based on visual appearance.
The following fields appear to be identical for every image file, so for simplicity sake I have omitted them from the main table.
If you were looking for these skintone files in s4pe, I would recommend searching by Memsize, as this is a number unique to skintones.