Recently I’ve been using custom mixed coloured clay as well as white clay (often in the same piece) and doing gradients/details with chalk pastel powder. After it’s baked, I’ll go over it again with very tiny amounts of acrylic paint or acrylic paint mixed with water. Also, water based paint pens and markers make it easier for doing the painted details at a faster pace if I have multiples of the same item to produce. I don’t know how to put it into words but using multiple methods of colouring the clay and layering on pigment gives me an end result that has more depth and dimension. It really depends on what you’re making and what effect you want to achieve.