There are a number of companies around that do kits for recolouring leather.
I had a pair of sports seats redone in leather about 3 years ago but my late uncle couldn't match the colour.
This week I took delivery of a kit to match the classic grey of my interior. It includes, cleaner, prep, leather colour, finisher and sealer.
There is even a small spraying kit included for the top coats!
What I didn't realise is that car seats are effectively painted and not dyed, therefore changing the colour is relatively strait forward.
I have been told that I can also use it to do the leatherette (seat rears) and trim. I'll post how I get on, but it'll be a few weeks before I finish the job.