Ok, I located the source of the problem. It's Google Sketchup, which I installed about a month ago. It adds a 'materials' tab to the standard Apple color picker and apparently this is causing problems with other applications.
The fix: (this comes from a Google employee):
The fix for me was to trash the NSColorPanelSwatches.plist in the user's Library/Colors/ folder. Any attempt to edit out the SketchUpColor entry in a plist editor ends up trashing the file regardless.
I removed the file and all is well.
Thanks again for your input!
Bob