One of the only cosmetic flaws on my car, other than some mild swirls and RIDS, when I bought it as a CPO in June were some scuffs/worn color spots on the driver's side seat bolster.
I finally got around to fixing it. I used a bottle of Color Flex from Magic Mender. They have a great selection of color tints to match factory color codes, and you can buy either the entire kit with the repair compound and the Color Flex, or just the Color Flex itself. I didn't get the whole kit, since I have no tears or holes in my seats. (Note: I would have bought something from Autogeek, since they are my go-to place for detailing supplies, but I couldn't find anything to do what I needed)
The Color Flex is water-based and can be applied with a foam brush, or a cloth, or pretty much anything you'd use to apply paint or stain. I used a small foam brush. It goes on easily, and dries to the touch within about 10 minutes. According to the instructions, it cures in about 24 hours. This was consistent with what I experienced.
My grey color went on and appeared lighter before it dried, and after the second coat it is pretty much an exact match to my leather. You can see the edges if you are extremely close and know where to look, but part of that might also be the fact that my car has had 4 1/2 years to age.
I am quite pleased with the results, it was an easy fix, looks great, and didn't cost much. Here are some before/during/after photos:
What I got - the bottle of Color Flex and 3 foam brushes - $24.95 + 7.45 shipping.
Seat damage: The color was worn off, along with most of the grain texture, but not much more than that. Note in the third picture, at the very top you can see where I put just a bit of the Color Flex on to test. It's just a dab, without blended edges.
Immediately after the first coat - you can see it's still damp. because the Color Flex is water-based, it's easy to control and dries very thin.
And here it is after the second application, with a dry time of about an hour. Note that I turned on my work lights since I was doing some other detailing, and forgot to turn them off when I took the photos. The work lights are causing that orange-ish glow on the side of the seat. The color match is actually much better that it appears in the photo - the flash really emphasizes the difference (partly also due to the texture difference, as well, since the grain is worn off).
As I said, overall I'm very pleased with the result. I'd recommend the Color Flex if you need to cover worn or damaged spots, and I would personally get the full kit to try if I had to fix a tear or hole.