You still should be able to clear this by my first suggestion. If this doesn't work, you can try to delete Users/yourusername/Library/Preferences/Finder.plist.
Another option would be to select another drive/folder or icon from somewhere else. Get Info>select icon>copy...Get Info on your RAID>select icon>paste.
You can also try to delete '.VolumeIcon.icns' from the root of your RAID in Terminal.app:
rm /Volumes/nameofyourraidvolume/.VolumeIcon.icns
This file might or might not be there. Just a stab in the dark.
You can also try to delete '.DS_Store' from the root of the RAID as well.
rm /Volumes/nameofyourraidvolume/.DS_Store
This file stores volume preferences and the like.
A simple reboot might clear it as well.
D.