I am using the backside of a white tone on tone right now in a little mini that I am handpiecing.
Also, I have often used the back as well as the front of a given fabric, if I like the effect of the (usually) duller backside, or if I need some kind of contrast that I don't have in some other fabric.
Incidentally, Kaffe Fassett said on an episode of Simply Quilts (so how long ago does That make it!) that he also does that whenever he wants to.