I find KTR's theory why T'Pol would wear her jump suit (to protect against the cold) a very good one. The jumpsuits I like the most are the red and blue one and of course the white desert one. Really liked the pic with Trip and T'Pol in desert uniform. T'Pol has one jumpsuit that has lines in the rib-area, I don't like that so much, because it make T'Pol more slim then she already is. The wedding dress was great. I did liked the colors, but still wonder what she would look like in red. Other personal favorite were her civilian clothes in
Carpenter Street (you know, the episode where she runs off with Trip to rescue Archer that had been caught by three Xindi Reptilians. O wait, that's my story.

)And her hair: I totally agree with Rigils post.
I haven't read every post in this thread, but I don't think this already been discussed: the meaning of certain outfits in a scene.
For example: in
Harbinger in the breakfast scene T'Pol is wearing outfit she never wore before nor did afterwards. It had wrinkled upward collar and it made her look like a matron - like she want to put distance by her choice of clothes.
In
Home T'Pol wears a beautiful blouse/shirt in different red shades with upward collar (my favorite) and Trip is wearing a very nice beige/white shirt (the "I don't want to offend any Vulcan and especially my girlfriends mother by wearing brightly colored shirt-shirt). If I am correct T'Pol wears that red shirt when she tells Trip she has to marry Koss and Trip the beige/white shirt.
In episode after
Home in the first scene the whole crew is in civilian clothes in the ready room for debriefing. They all looked like they just arrived - including Trip. But the wedding has been at least two weeks ago and I don't think he would stick around.
So why wear the clothes of Vulcan (same goes for T'Pol, why the red shirt), remembering you of that time? Trip doesn't care what he wears? But he had chosen that shirt with a lot of care. Also, if Trip had return to
Enterprise he had plenty of time change to his uniform.