A proper dye job is always the best way, you'll need to strip out the conditioner from the saddle and then Fiebings should have a dye product etc. A saddler or a specialist dyer (I have used The Dying Lady, yep, with that spelling!) on Facebook and she did a decent job on a natural tan saddle that was never going to sell. I'm no expert, but I know we've discussed it before, have a search in here for dyeing a saddle. "Consumer" top up type products were mentioned, I have no experience of them but a few people have rated them.