Hi:
In prior versions of Office, I think that you only have a palette of 56 colors with Excel (like 2000, 2003 and even 2007). It's not until Excel 2010 that you have all 16.7 million colors. So that means browsers will show more "accurate" colors than earlier versions of Excel. For example -- a color that is defined in hex as #6495ED (light blue) will show as blue in the browser, but is mapped to a more purple/lavender color in Excel 2003 and 2007.
You'll have to look up the 56 colors that are acceptable to Excel. This site isn't a Microsoft site, but they have some history that goes back to Excel 97 and colors:
http://www.mvps.org/dmcritchie/excel/colors.htm
This page talks about how to change the palette, but doesn't show the default palette:
http://support.microsoft.com/kb/288412
cynthia