My 17" iMAC G5 has suddenly developed a problem with its Desktop graphics. This involves the Dock, Folders on the Desktop, and pull down menus. It appears that colours are dithered, the colour display running at 256 colours or perhaps thousands of colours - in these areas ONLY. Items displayed within programmes and folders displayed when you open a folder from the Desktop are perfect. However, pull-down menus within a programme also have dithered graphics. Below are some screen grabs to show what I mean. I have tried re-installing OSX 10.4.11 but the problem remains. I suspect something is conflicting with the Finder. Does anyone have the same problem or know the solution?