You get 56 colors in any workbook.

But you can change those 56 by:
tools|options|color tab|click modify

You can read lots more about how excel works with colors at David McRitchie's
site:
http://www.mvps.org/dmcritchie/excel/colors.htm

Bob Tourkow wrote:

In Excel, is there a way I can lighten the fill colors in a cell? That is,
can I "customize" the colors in the "standard" Excel fill color palette to
lighten them?

--

Dave Peterson