I don't know what happened, the Finder icon on the dock just got translucent and ugly. I tried restarting the iMac, but it stayed that way.
What did I do? How can I fix this?
Does this also happen if you are logged in to a different user account?
I only have this one user account, but I created another account just to see and yes it only does it on the main account.
That result indicates you have a bad file somewhere in your home folder. Look in Home/Library/Caches for anything Finder or Dock related, trash it, and then log out and log back in.
It might also be a problem in your Home/Library/Preferences folder. Start with the Finder and Dock preference files. Instead of trashing them, move them out to the desktop, then log out/log in. If the problem persists, put the files back and try moving out other prefs files. Repeat until the problem disappears, and then just trash the bad pref file from your desktop.
That did the trick. I moved com.apple.dock.plist and com.apple.dock.db from the Home/Library/Preferences folder and logged out and logged back in. I had to put a few apps back on the dock, but the finder icon is back to normal. I guess I'll just delete these defective files.
A quick followup. Marcel Bresink's TinkerTool System app has a very nice clean process for troubleshooting exactly this sort of problem. First is asks you to shut down the running apps whose caches you suspect. Then it moves aside the existing caches, gracefully logs you out. You log in again and it picks up where it left off. If the TEMPORARY cache removal fixed your problem, it allows you to proceed to delete them. If not, it restores the original cache settings. Very orderly and reliable.
Finder icon got ugly.
