Ahh but that's not the end of the story though, sometimes you have to work a little opaque on top of a transparent, usually for hi-lights and such. I'm of the school of thought that you borrow from this and that technique to achieve your end result. Not be stuck on the technicalities of just one. What I like to do is do a monochromatic underpainting in black and grey (overreduced paynes grey, I don't like using black), then add color glazes (transparent) over that and then reiterate the hi-lights with a tint of the color you are hilighting. (tints being the base color with white added).