People are asking. I’m answering:

Cycle Blending Modes Backward: Shift and -
Cycle Blending Modes Forward: Shift and +

I’ll write a comprehensive post on Blending Modes soon, with extra Mathy Goodness for all you compositing geeks out there. If you’re too excited to wait, go get and read The Art and Science of Digital Compositing by Ron Brinkmann. I was very excited to note that there is a second Edition, and One-Clicked it right away. The First Edition rocked. Thanks to Lexi at Sterling-Rice Group for getting me to post on this subject.