The pigment has worn away to the leather underneath and will need replacing. Balms or colours of this sort will not repair this problem although some may make it look better. It is a two tone leather (ie one colour on top of another),or at least it looks like it on this photo though sometimes it is not easy to tell from photos and balm type products will make the area look very different from the rest as they are only a one colour application.
We have tried balms to replace two tone colours where the top colour has come off and these simply do not cure the problem.
To fully repair you would need to use a restoration pigment and refinish. There may be a need to fill some of the damage (it is difficult to tell from the photos) and this is always a bit tricky on seat panels as it may not last due to the constant flexing. The fact that it maybe a two tone also would make it more difficult to repair as replacing the two colours can be tricky if you are not used to doing it.
I would seriously consider carefully whether to take this job on as it looks well worn, may have grease in it and would be difficult to guarantee a lasting outcome, this is just from the photos, real life may be different!!! Panel replacement is always an option if the customer is very keen to keep the suite.
Hope this helps