We've gotten a bunch of reports from you fine folks today regarding your Gmail apps causing a screen flicker, and being unable to get to your inbox. We never experienced it here, but that doesn't mean it wasn't happening, as forum threads were popping up all over the place.
Google's just gotten back in touch with us and says a fix is on the way. Googler BrittanyBee explains thusly in the Google Product Forums:
Beginning this morning, we've received reports of a bug causing some Gmail users on Android to experience screen flickering when they open the app. We are in the process of fixing it and the issue should be resolved shortly. We apologize for any inconvenience.
Glad to see they're on it, but that's a pretty big whoopsie. (And believe us, we know about whoopsies.)