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

The fill color, the fill pattern, or the line color of a WordArt or
AutoShape object in an Office document does not change
http://support.microsoft.com/default.aspx?kbid=833258


Steev wrote:
When I try to fill cells with color, the shading doesn't show onscreen, but
it does show in both the print preview pane and in the printed document. How
do I enable shading onscreen? I am using Excel 2003.


--
Debra Dalgleish
Contextures
http://www.contextures.com/tiptech.html