Description of problem: The summary says it all, the change to a black background causes problems for lcd monitors connected through an analog vga cable. The charge background is the first image shown directly after the mode change from loading the kms driver, and since it is all black the monitor is having a hard time figuring out the exact size / timing and ends up assuming / detecting an other resolution then the one actually used, with a distorted display as a result.
Clearly we should use the background X gives when you run with -retro
i'll put it back to blue for now