No, I think its the same but different...look here a sec.i think that he looks as he does when he's palpatine, all the time. Then when he really uses the darkside of the force, since it IS stronger (as said by GL), it just takes so much out of him and his appearence ages rather quickly. Since SW is like religion on steroids, it could be like when Moses saw the burning bush and aged like 30 - 40 years just from the power of God, ya know? (and no im not saying God is anything like the darkside of the force)