I want to use a pre-made set of hands for a character I'm creating, but they aren't the right color. How can I change the color or download all the hand pngs to edit and then re-upload them?

If you are using pipeline version, you can edit external .PSD file editor software.
Then you can change color or edit hands.

If your image editing program is Affinity Designer,
this might help:-
https://www.youtube.com/watch?v=sRpRKvtsSY8 

76% of original size (was 661x19) - Click to enlarge
YouTube Tutorials Here