acrylic or oil,, will hold the color without fading,, natural pigments are an option as well,,
I like oil because it is a little more organic,, and the colors are easier to tone down(to look natural) , and still have a brilliance and depth of color,, a drying agent can be used to speed up dry time,,
every one has a favorite, just like artist that paint canvas,, each has a different approach and preference of medium depending on the look of the final results,,
