Fixed Green Detection, tested remove-red.
Fixed Green Detection, tested remove-red.

Somehow the subtraction in green detection got flipped around, so it
wasn't detecting certain green changes. It was detecting some other
green changes, which confuses me, but it looks like it works on both
sets of cases now. Also, I tested remove-red for simple, supported cases.

jackfirth/herbie,jackfirth/herbie,jackfirth/herbie,jackfirth/herbie,jackfirth/herbie,jackfirth/herbie