I have always said: "White is not a leather color - and that goes for all the colors that contain white (grey, pink, sky blue).
One nice way to get a grey color on leather is very old, or very newly made, vinagroon (ferrous metal dissolved in vinegar).
I have a separate Blog Entry all about that.
Here is a video where I play with vinagroon that is more than ten months old and three day old vinagroon:
After the leather dried and I applied NeatLac to each piece:You will notice not all the pieces ended up deep black even after the new vinagroon was applied. This is due to two factors: 1. The leather can have different levels of tannins that react with the vinagroon. 2. I simply needed to get more vinagroon onto the leather to give a more completer reaction.
Warning again: DO NOT NEUTRALIZE the vinagroon - the leather has to stay acidic (about pH of 4).