I would say your best bet is to use oils to paint them. Oils blend really well and you can really use them to get the different shades and highlights in coats that you cant really get with other types.
Apart from that I would say... get references, go online find pictures of the animal in question and save it. open it in paint, use the dropper to get the different colors and make a pallet on your computer.
THEN you print out the pallet, not the picture, and mix your oils on it, to make sure you get the colors correct.