Re: Skintones glitching, having strange patterns
What that looks like is broken CC. Probably something older too that predates Island Living, if I interpret what you said correctly, it only shows up when the sims have a tan. Try stripping them completely in CAS and giving them new everything. I mean everything too, CC body details, makeup, jewelry, tattoos, accessories as well as the clothes and put them in all game items. If the issue goes away, then it's CC. Tbh, those are very distinctive marks showing on the sims in your pics and you might be able to find the problem if you can figure out what CC you have that has those markings. Since your pics appear to be in CAS, you might just have to remove items one at the time until the marks go away and then you'll know what it is. Once identified, then you can remove whatever it is that's causing it from your mods folder, so it doesn't happen again.
Also, you should delete the localthumbcache.package file whenever you add or remove CC so you might want to try that first so any remnants of whatever was removed will be completely removed from your game.
Hope this helps.
