Leather is a whole can of worms. You have to prep the leather right and get the right products. The issue for me has been matching color and sheen (matte/gloss). I think because your backseat is rarely used, that's why it's hiding up.
Prepping the leather involves cleaning it well removing enough of the coating for the new colorant to "bite". The coating can be removed with 800 grit sandpaper, then followed up with a lighter grit. Then you have to clean it with something like benzene or IPA so its free of all cleaners.
Then you apply the colorant, and the "clear coat" on top of that. Application shod be done to a whole panel of leather for best results, and the dye and coating should be applied with an airbrush.
I did all this once and didn't have an issue with the bonding of the products, but with the color match. Besides the right shade of color, you have to get the matte/gloss sheen right. I can be hard to tell what is "off".
The products I bought were from Furniture Clinic in the UK. I've considered doing the panel over many times with the Swissvax Leather Healer, but the cost is very high. As you need their prep stuff, colorant, matte corrector, gloss corrector, etc... And since everything from Swissvax is a hundred bucks, that's a big investment to gamble with.
