I draw the webcomic Manly Guys Doing Manly Things and work on cartoons you might see on TV sometimes.
I used Angelus Paints. They’re water-based acrylic so you don’t need any kind of special solvents to clean them up, and they’re specifically designed for decorating high-stress leather like shoes, jackets, and bags without cracking, chipping, or peeling.
The website looks super sketchy, but they came highly recommended. A little goes a long way, too. I got a four ounce bottle of the vanilla shade for doing that skull and only ended up using two capfuls.