Hi custom content creators!
As you might have noticed, in Island Living sunbathing supports tan lines from whatever clothes your Sims are wearing. Tan lines will work with your custom content as well (so long as you set it up your alpha channels properly).
* Please note this does not work for accessories. The only accessories that do support tan lines are socks, tights, gloves, shoes, and full-helmet-hats.
The alpha channel of the diffuse texture is used as the mask for applying a tan. That means in order to get good tan lines, be sure that your alphas are properly aligned with where you want a tan applied. On our end, the game does automatically apply a slight blur to the edges to make them feel more natural, so you don’t need to worry about doing that yourselves.
Concerning CC Skintone Replacements: Tans/burns are overlays on top of our basegame skintones, so it’ll work on replacement skins that are roughly the same complexion and in the same order/slots.
Hope that helps, and feel free to let me know if you have any questions, and I can try to get you answers.