I've just thought of two more ways people can help, and I've added them to the appropriate page.
By the way, people have been sending in pigments, expect to see some more soon! Some of you may have noticed a few on the repo already...
Yes, Epidermis needs to be tested, just like any other program. We've written up a test case for you to tackle. If you find any bugs, you know where to report them!
If you're desperate to put your cash to good use and donate to Epidermis, may we redirect you to Stani's Python Editor instead? Epidermis' main developer (actually, only developer at this point) uses it a lot, so helping SPE would be helping Epidermis.