This has been happening for a while. But originally i only seemed to notice it when using my external apple cinema display. Certain icons seem to not always display correctly. For example, the volume icon that pops up when you change volume. Sometimes it's normal. Sometimes it's dark purple. Sometimes its dark purple then flashes white before it disappears. Currently it's white, then goes black before it disappears. It seems to change every time i restart. Other things do strange things, but aren't at the moment. E.g. the application icons for each application window in mission control. Sometimes these are very dark, or just show white noise (????) I have no idea what is going on. Any advice would be appreciated.