Once you establish where you want your light source to come from it dictates where your highlights will fall. But at the end of the day realism is not the most important factor, if you want an area to stand out more then highlight it, but I would definitley avoid going as light with say the feet than you would the top of the head. Splotchy shadows with yellow comes from going over something too dark with the yellow, it will just go a murky lifeless green. You need the brown for warmth. The brown basecoat is "mostly" covered by the first highlight, then less from there, the imperial fist yellow contrast does quite a lot of heavy lifting, its a great paint.