S/V's FD emphasized sharp moves, so she might have wanted to emphasize strong contrast by dyeing her hair black. Brown/reddish brown hair softens her apparence. It may or may not go better with her skin tone, but notice how sharp the contrast with her gold dress. Wearing her black hair in pony tail also made her look sassy. Personally I loved her look!
I personally preferred the orang and hot pink dress from 4CC to the worlds gold dress. It did not flatter her figure AT ALL. And that says a lot, considering her figure...
To me she looks fabolous no matter what she wears and no matter what hair color she picks. Honestly I think she is one of the most attractive women on ice, also because she can look very different each time I see her, yet she is always captivating. Just an example - Kiira Korpi is very beautiful, but unlike Tessa, she always looks exactly the same to me. And i cannot imagine her having different hair color/style than she has had for years.
Plenty of skaters go darker when skating to latino music, so maybe that's why she changed to a darker tone. (I don't think it quite qualifies as black.) She may have also just wanted something different. I think the colour change was also more noticeable because her style for the FD was very plain-just a pony tail. She usually has it done a bit more elaborately.
I also preferred her 4CC dress. The new one was nice, but didn't seem to be tailored quite right for her figure. She does look great no matter what, though.
Serious, I was also mesmerized by her hip movements, and I'm female. That woman can move.
I believe I read in one of the interviews that the darker hair + ponytail was because they felt it the look went well with the Latin FD they were doing.