Vinegaroon is acidic, sodium bicarbonate basic.
I know very little about leather, but quite a lot about the protein fibre wool (and hair, and silk). It stands up to acids pretty well, but not to alcaline substances.
Given that leather is protein-based material, I would expect somewhat similar behaviour. I also wonder whether plant dyes used normally for wool might work - the above recipes for leather use some of the same plants. Brazilwood, saffron, tree barks, wold (Reseda luteola) - does anybody know what fustic berries are?