Hm... After seeing his alternate costumes and reading his bio I kind of thought:
What if, the dark haired costumes are from his time as "a normal mortal" and the white/silver/blond haired one are after he's been given the status of immortal/god?
I really like the idea and will probably stick with it ^^
It would kinda of fit.
Also it would go along with my theory about his "arrogance" and "cookieness", that I personaly kind of like.
I REALLY hated that he got landed in Shu thought.
Due to the biography I had hoped for him to somehow end up in Wu. 1) because most of my favourites are Wu-ers and 2) because I'd love to see some interaction between him, Lu Xun and Lu Meng and later Lu Bu.
I dimly remember that one or two of those Lu's are his descendants and would have loved to see some "family" interaction ^o^. If you read the bio, you'll be able to figure that out for yourself too

Also I'd have wished for a bit more bantering between Taigong Wang and Zuo Ci. I know there was some, but at the same time I felt it ... lacking something.
All over I have to say despite so many time having passed since I played WO2, I still like this character very much. I'm looking forward to finishing his costume and representing him in september. ^^