[Soultrader]

The green means contracts at the ask and the red means contracts at the bid. So in a fast market, you may see alot of market orders at the bid indicating panic selling. After a decline, look for contracts at the ask which would indicate short covering.

White prints are transactions that take place in between the bid and ask. It may sound off since the YM trades at 1 pt intervals. But let's say the bid is @ 17000 and the ask is @ 17002. A trader sends a market order to buy but is filled at 17001. This 17001 print would show in white.

I believe the + and - signals are just indicating whether the current print was a uptick vs downtick from the previous print. Hope this helps.