If you're playing Chris Sawyer's excellent game, Locomotion on Windows Vista or Windows 7, then you may experience after a minute or so ingame, that all the colours go all purple and green. Don't worry though, don't uninstall the game or chuck it away - you can still play it!
The problem is caused by the way Windows Vista and Windows 7 deliver the colour palette and if (like many) you have an image or a slideshow desktop background, then this is what's causing your problem. All you need to do is right-click on the desktop and select "Personalize", then just change the desktop background to a solid colour (any will do - I usually just use black), then Apply the changes and then fire up the game and hey presto(!) you have no graphic problems in Locomotion.
Simple solution, for a simple problem. :)