: Most polys can be tinted with Universal Tinting Colors from a paint
: shop

I tried that and had poor results. The pigment particles in the tint are too coarse and tend to settle out of solution as the varnish cures (this is probably less of an issue for an opaque skin than a translucent one). Artist's oils have much finer pigments that stay in suspension and produce a more even color. About the only advantage I found to the universal tints is that the paint store gave me the small amount I needed for free, but I guess I got what I paid for.