My friend Gary Arvidson is a remarkable man - well into his seventies he has a major amount of unadulterated fun with leatherwork!
He came up with these five nice dyeing/staining/sealing effects:
1 First cover the leather with smoke black Hi-Lite Stain - 50% diluted with water. Then a layer of Green Cova Color diluted 50% with water, followed by a mix of [40% Gum Tragacanth + 40% Green Cova Color + 20% water]. Finally finish with a mixture of [20% Silver Cova Color + 80% Neatlac].
2 First cover the leather with smoke black Hi-Lite Stain - 50% diluted with water. Then a layer of White Cova Color diluted 50% with water and a layer of Yellow Cova Color diluted 50% with water, followed by a mix of [40% Gum Tragacanth + 40% Green Cova Color + 20% water]. Finally finish with a mixture of [20% Silver Cova Color + 80% Neatlac].
3 First cover the higher areas with smoke black Hi-Lite Stain - 50% diluted with water. Then a layer of Brown Cova Color diluted 50% with water (here you can play around with various different brown acrylics), followed by a layer of Saddle Tan Hi-Lite Stain - 50% diluted with water. Then a layer of Copper Cova Color diluted 50% with water. Finally finish with Neatlac.
4 First cover the leather with smoke black Hi-Lite Stain - 50% diluted with water. Then a layer of White Cova Color diluted 50% with water, followed by a mix of [40% Gum Tragacanth + 40% Yellow Cova Color + 20% water]. Finally finish with a mixture of [20% Silver Cova Color + 80% Neatlac].
5 First cover the leather with Light Blue Cova Color - 50% diluted with water. Then a layer of Royal Blue Cova Color diluted 50% with water, followed by a mix of [40% Gum Tragacanth + 40% Turqoise Cova Color + 20% water]. Finally finish with a mixture of [20% Silver Cova Color + 80% Neatlac].
I hope this inspires you to experiments of your own!