Many leatherworkers use Vinagroon to get leather black or grey.
There is another option: getting the leather brown using Potassium Permanganate.
Here is a volume cover I only decorated with this method - I used a split, so the work was all done on the "flesh" side of the leather.
Keep in mind I made this cover in the eighties - no fading, because there is no pigment involved.
The back is just a flat colored silhouette.
Here is a short video showing it being