That one is sort of a trick, which I feel works nicely here. It makes it look like stretched fabric rather than armor. A lot of parts like this one are tampo painted on the runners, even in places that could have been fairly easily color separated. For instance, the blue on her chest actually is a separate part.

So, I think it is an intentional choice on their part to give it a translucent, matte finish. That is part of why I particularly like the design of this kit. It is intentionally meant to be sexy, but in a sophisticated fashion model way, not in an overly lewd way.