I've been playing my sims games with a certain CC skin tone that is for all skin types since 2016. I've never had an issue with the skin tone transferring over to a new occult type or anything till no...
The most common culprit for this is No Ea Eyelashes. If you still have issues, check this list: https://forums.thesims.com/en_US/discussion/comment/17116992/#Comment_17116992