Since protools 8 i've had this intermittent bug that when you select a region sometimes an accidental mouse drag or other trigger occurs and the entire session is selected and goes into reverse color scheme. the only way to get out of this mode is to select another spot on the timeline. sometimes it takes a few tries to actually get it to stop behaving this way. sorry its not repeatable, its hard to know when its going to happen but it is annoying.
Idea No. 1461