I just tried something, and it seemed to work pretty good, so I thought I'd pass it along.
I have a large leather tank bib/pouch, and it has sustained alot of sun bleaching on the "high points/rolls" of the bag. It has a rubbed finish that requires saddle soap, or another type of neutral color leather conditioning. Due to the sun, the black color has been bleached out in some areas. The only thing I could think of was black shoe polish, but I didn't want a shine. Then I hit on it!
I rubbed in the black polish liberally, to get the color back in the leather. Without wiping it off, I went over it with a neutral color leather balsam, that has the consistency of toothpaste. That provided the moisture to drive the color into the leather. I've applied 2 coats of the balsam, and wiped it down to take the film off. The shine is to a minimun, and it's back to an even color.
I've never seen this mentioned, and I thought it may help someone.