[Benji]

I believe the background behind the woman in the image you questioned is naturally that color. My best guess is that the wall outside that window is painted that color and it was lit by natural daylight.

As far as putting a colored filter across the lens then using a different colored flash to cancel it out, I would say no. There are three primary colors, so you would need all three in an image to color balance the skin. You could I suppose, light the subject and background with flourescent light then gel your flash with an FLD filter to cancel out the green light from the flourescent light. Everything lit by the flourescent light will be green, everything lit by the flash will be correct (color temperature wise anyway) but that sounds like a lot of work to me when it could be done in Photoshop with a few mouse clicks and a few minutes of time.

Benji