You're going to have to use some VBA.

Chip Pearson explains it:
http://cpearson.com/excel/colors.htm

As alternative.
Add an extra column and put an indicator in that column (X). Then use
format|Conditional formatting to make it look pretty. But use that indicator
column in you calculations (=countif() or = sumif() or ...).

Mike K wrote:

Within an existing worksheet I have a column of data containing cells that
are either highlighted in yellow (manually highlighted) or not highlighted in
yellow. I need to sum how many cells are highlighted in yellow and how many
cells are not highlighted in yellow. I'm running MS Office Excel 2003 SP2.

--

Dave Peterson