3M “5200" polyurethane adhesive/sealant is available in White, Black, Mahogany, & Tan, completely cures in 5-7 days with no shrinkage; after which it is paintable. In fact 5200 will even cure under paint (& water), so might be overpainted after a 48 hour set.
I wouldn’t play with the chemistry, trying to colour it.
I know it's not the same, but I've heard of people who have taken silcone sealant and poured coloring into it, most memorably, lime jello. They were trying to make a new fishing lure by coloring it and squirting it into a mould made from a bar of soap.