How to clean leather straps?

agree its a bit pointless. The question was more because they are double straps and one I forced through the pedals (with bit of oil, dirty hands, etc.) so that looks grey and messy and the other looks still brand new. Just my obsession with perfection. I know you guys will say mess up the other one as well but if someone has an idea let me know.

Nothing will work. As a long shot, go to a re-upholsterer and see if he has any leather touch up colours. He will want you to remove them from the pedals, and back to square one. With a bit of riding they will all be shitty in no time anyway.