Thank you very much for your comments about buffalo colours. Yes, most of the pictures of water buffalos are about dark grey animals, but there are grey/dark brown with beige belly and legs too. I choose that colours because are more atractive for the wiever than the all dark buffalos.
And about the horns, the painting is on progress, they should be painted with shadows and lights...
An example of animal with beige belly and legs
Really, I even found pictures with a buffalo in white and brown colours, just like a european milk cow ¡¡¡¡¡