I've various systems in my company, which is running with Office XP (Outlook alone is 2003 & O/s is Windows XP). In one of the PC, some of the excel files are giving problems by changing the colours automatically. Only common thing I could observe in those files are that they've used some basic colour formatting (bold / font & background colour changes etc...). The issues are like white colour background automatically changes to ash colour, some cells change its background colour to yellow and font colour changes to white etc... This is a not a every day problem, but yes, it comes out every now and then. We've changed the system, whereas the issue seems to be continuing even after that. There are other systems, which runs with similar software combinations, whereas the issue is so far seen only in this computer.