Ask a leather furniture specialist. They have conditioners and may have colorants.

Leather dye will do the trick BUT......
It may be lighter/darker than the rest of the couch and cause it's own problems!! Not all leather is created equal ;^( and parts may take the dye differently.

I've used leather dye on our large leather sectional to cover cat scratches that had ripped through the leather. It worked well, and the repaired areas are not visible in shading or appearance, fortunately. I don't know, however, whether this application would work as well on larger, discolored areas, because of natural fading or discoloring of the original finish.

Our couch is ivory colored, and the product I found matched it perfectly. I've pasted the link of the product I used. I have no association with this company, but did want to say that we were very pleased with the final outcome. As I said earlier, the color matched perfectly and you cannot tell where the repairs were made.

Here is a link that might be useful: leather magic

Good points and help everyone, thanks. Thanks for the link, Nanny.

It's deep espresso brown and it's a high end set, so I think I'd be alright trying a color, but who knows. If it wore evenly it wouldn't bother me that much, but it's annoying that it's one sitting spot on each couch! I keep telling everyone that we need new 'favorite' spots and to move around but it's too late!

Can you move the cushions around?

Nope, not movable. One arm rest on each couch is fading too though, so that wouldn't help with that problem!

This may be totally off...but Nate Burkus suggested aging leather when it started discoloring. He uses sand paper on areas like you would distressing a piece of wood furniture.

My leather set did the same. I think it has to do with different people who use the furniture. The one place my older son sat all the time was my culprat. I gave up on leather, but certainly would have tried the distressing before making changes. Looked up Nates website and he doesn't have anything explaining how to do this.

I use Tandy Leather store. We have one locally. They sell permanent dye that can be applied with a cloth or dauber. Then a matte sealant, then a conditioner to soften the leather.

Here is a link that might be useful: Tandy online catalog....

I have a natural leather sofa and I use leather shoe polish on it. I rub it in and then wipe off any access with a clean cloth. It doesn't rub off on clothes. Try it on a small section first and see how it does.

The product in the link might work. I've used it on leather boots and just yesterday some leather barstools. It will darken the item considerably. I have a leather recliner I want to try it on, but haven't worked up the courage yet.

Here is a link that might be useful: Obenauf's Leather Restorer