minispace's method, I think, works really well, and can be easily improved on by, say, adding eyes and clothes and stuff, after, so that they aren't coloured by the tint. An example layering system being
basic head shape/silhouette + ears/nose/chin/cheeks/brow + skin colour tinting + eyes/hair/facial hair/mouth/eyebrows/anything you don't want tinted + clothes + accessories. All of which, of course, would be inheritable, clothes and accessories aside. Clothes and accessories could be changed depending on culture, but the rest should be straight inheritance matrices.