If the high contrast setting is turned on you won't see the fill colour.
There's information in the following MSKB article:

Changes to the fill color and the fill pattern are not displayed in
Office programs
http://support.microsoft.com/?id=320531

sonny wrote:
color fill on my microssft excel2003 not working, would like to know how to
repair it


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Debra Dalgleish
Excel FAQ, Tips & Book List
http://www.contextures.com/tiptech.html