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


JackBScott wrote:
I'm using Excel '03 and filling cells w/ a color (with the paint bucket).
The color does not show up in my spreadsheet, but does show up when I print.
Every now and then I get a fill color to show up in the sheet, but if I click
in another cell, the colored cell goes back to white.


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