This started happening to me after upgrading to 11.3 - Black on black panel colouring.
Sometimes the problem seem to fix itself after fresh login or reboot.
I was looking for some setting that would shake it loose, but never guessed that
changing the size would do it.
I have an Nvidia 6600, so it’s not card related. And I think its happening on
xming remote logins as well.
Using remote X from Xming results is a slightly different problem - the panel is almost 100% black on black - Graphical effects need to be turned off in configure desktop -> Style -> Fine Tuning -> High Res Low CPU
That’s work great for me. My panel and command dialog (Alt+F2) being strangely colorized (desktop effects refuse to start too) after some manipulation in desktop settings (openSUSE 12.1 with KDE). But now this is correct and problem is fixed. Thanks caf4926!
:good: 
No worries