When they grow up they are all a skintone that they should be IE dark for dark parents and mixed for mixed parents. Also its affecting my sims whatever skintone they are, I thought at first it was only happening to my mixed babies (1 parent light, 1 parent dark) but then I had 2 dark parents have a mixed skintone baby changing to pale as well when removed from the bassinet. This is only happening with the babies born with the medium skintone they are being changed to the pale skintone when picked up for any interaction. Then I removed my entire sims 4 folder and played through 6 sim days for 2 pregnancies and the same thing happened so I don't believe this is related to mods. I did have custom skins for babies installed so I removed those mods and tested and it still happened. For the boys there clothes are changing but not their skin color. So far this is only happening to my girls. My baby's skin color is changing as they are being removed from the bassinet.
If you’re opting for an extra natural look, this Salome skin is for you. I checked the list of reported issues and don't see this but it's possible I overlooked it. Kaastar Gaming have been exerting a bunch of effort on creating skin overlays for the Sims 4. Information, Guides and Announcements for the EA app.