when I press command-Tab to get the task switcher icons, to let me change the foreground program, I am seeing that after a little while, the icons are badly miscolored. Anybody else seeing this bug? Thanks.
Yes, I'm seeing the same problem on occasion. For me it happens mostly often when I connect an external display - the switcher looks as though it's underneath a semi-transparent black overlay. Restarting Dock.app (which runs the application switcher, as far as I know) doesn't help, but rebooting the laptop with the external display still attached does.
I've reported the issue to Apple (using their bug reporter) and have been informed that it's a known issue. Hopefully there will be a fix soon.