Literally just tattoos and lighter skin tones.
Forest trolls I guess could technically be done by giving Darkspear more skin tones, but I feel a full fledged AR would fit them better. Just like Ogres, which would require an entirely new rig, along with a female model.
The amount of effort needed to make an entirely new rig like the Ogres is why Ogres aren’t in yet, and the Wildhammer are.
Also if they give Ogres to the Horde, they need to give an AR with an equal amount of effort put into it to the Alliance.