All the information is here:
You’ll get both the natural and unnatural swatches, you can remove the ones you don’t want with, for example, Sims4Studio.
It’s a ‘soft’ birthmark because the transparency is 50%
Can be found in skin details, near the freckles.
No custom thumbnails, but not hard to find.
Disabled for random.
Made with Sims 4 Studio.