Whatever you do, don't let it get soaked. It can warp your frame, crack it, and ruin the tone. The leather can shrink too. When you are applying stuff, use as little as possible, let it dry thoroughly, then add more. It may take longer but the drum won't get hurt.
As for colors..... Think of things that stain. Red wine, tobacco juice, walnut hulls..... etc etc. Maybe try soaking some coloring agents like turmeric in oil, draining and filtering the oil, and practicing on scrap leather? No matter what you try, practice on something you don't mind losing first. Preferably something close to your drum surface so you can see how it'll react.
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