Tough break. Sad to say, but anything that goes in the overheads is usually going to get a battering at some point. Maybe some Obenaufs LP if you have some as that may darken the leather down a bit ?? There are going to be leather dyes that could be used. I'd use a lighter shade and build up in many applications to try to match the rest of the strap. Never done such things myself as always scared the dye or polish rubs off onto clothing.