Star Trek: 10 Secrets Of The Enterprise Uniforms
2. UPN T&A
While Jolene Blalock publicly praised T'Pol's Vulcan catsuit in Enterprise's first two seasons, her sentiments about the character and her wardrobe seemed to shift by the third year.
Along with a change in tone and story, Enterprise season three introduced a new look for the now civilian T'Pol. Designed with input from Blalock, T'Pol's new costumes featured bright colors, a plunging neckline, and a fit which "hugged Blalock's supermodel-esque figure".
According to Robert Blackman, the reason for T'Pol's career change and the new costumes was simple:
The ratings dropped. That's the frank, real answer... There wasn't enough raw sex appeal.
Following the completion of season three's Xindi arc, T'Pol received a Starfleet commission and the rank of commander early in season four. Along with her new role came a new Starfleet uniform... but only kind of.
Rather than adopting the standard Starfleet jumpsuit for the character, the costume department opted to modify T'Pol's existing causal attire. This adapted Starfleet uniform included the standard NX-01 mission patch, commander's rank pips, and sciences blue division color piping on the shoulders, while keeping the aforementioned plunging neckline and tight fit.
It's unclear exactly why T'Pol wasn't just given a regulation Starfleet uniform, but it probably had something to do with the whole "raw sex appeal" thing. Regarding T'Pol's costumes and the treatment of character overall, Jolene Blalock did not mince words:
You can’t substitute !*$% and ass for good storytelling. You can have both, but you can't substitute one for the other, because the audience is not stupid.