I was able to edit the archetypes by Cmar’s TS4 Skininator ()

…in most cases,it’s supposed to be…but sometimes,seems baby has dark skin tone. This skin tones are handled as a light skin tone,so if parents have the custom skin tones,babies will have light skin tone.

Babies don’t have custom skin tones,so they are usually just a base game color,and custom skin tones will appear after baby grows up into a child.