Be it green or black, the troll should be totally bald and his skin should have warts and knolls in little clusters. Legs will always be pretty much the same with knobby knees. Sort of a battle cry thing. Ears stick back, not outward. Look at a few fantasy pics.
Eyes are slits or pointed.
Don't make them oriental or anything, that'll suck. They should pierce and could be yellow or white. Straight white or yellow would look excellent if you could pull it off without looking too cartoonish. They should be tight but exaggerated. In other words, make Troll boy 'bound' along.