...You could just grab a screencap from within Zbrush. That's a gradient from Dark grey > Light grey, which fixes what people were complaining about, and if you choose a good matcap prevents the model getting lost in the dark.
i would love an update on this... when i render a picture, and go to bpr passes to get a render out, no matter the background i have on my screen, in the bpr render theres a black background. i know its possible to change this within zbrush. just not how. i would love an update on this...