I have had similar issues with my Bold 9000 as well.
Sometimes the screen is completely white other times it looks like a scrambled channel on a television. Going to a different screen (hitting the menu button/locking and unlocking the screen) fixes the problem.
I have wiped the device using JML and it continues to do it. The issue is erratic and annoying at times but I haven't been able to pin point the problem.
I'm thinking that it is a hardware related issue, but I'm not sure.
Pearl 8100 ---> Curve 8310 ---> Pearl 8100 ---> Bold 9000