Actually, for me, the screen is the number 3 item for killing battery, trumped by phone calls at number one. And I dont even spend that much time on phone calls, usually less than an hour per night (I wish I could find a solution for this besides not making / taking calls).
Under Settings->Display->Auto Adjust Screen Power, I have this DISABLED.
This helps significantly with the 'greys' on a dark screen (to the best of my limited comprehension, this is being called black crush?) AND virtually eliminates the 'banding' I was seeing initially. Strangely however, I had to disable this option and it took a day or two before the banding almost completely disappeared (I was seeing it ALOT on the Google Market initial grey screen before it loads in the ads).
I use Auto Brightness.
I also have Settings->Power Saving->All Options are DISABLED.
Anyway, you might try disabling the power saving and auto adjust screen power and see if that helps with black appearing grey using the app you are mentioning.