The magic trick of using flash is that you can turn into black background even a white wall ;-)
But I guess it is not the case here, because white umbrellas are modifiers quite hard to control, and they spills the light in all possible directions :-)
@perfectsense - cool photo.
The only thing that hurts my perfectionist soul is non-symmetric shadow on the collar. I guess you used small flashes - so no pilot lights available, and it's really hard to fine-tune everything. In this case I would probably do a mirror of one side in PS ;-)
Oh, you are picky. I didn't notice the shadow on the collar. Noted.
Thanks! Yes, I used small flashes and it is very hard to get your model posed exactly in the middle to get perfect symmetry. That shadow was killing me too, but why I did not mirrored it? Simply great idea! Thanks @adamdo