how can I use shading as criteria in a formula?
 

I'm using Excel XP and I'm trying to set up a 'Total' cell that will be added
to if a cell is shaded in a certain color. For example, I am tracking my
used sick and vacation hours and want to add up the hours used for each. My
spreadsheet is set up with each month in a separate row, with a column for
each day of the month. I mark the hours in the appropriate day and use one
shading color for vacation hours used and a different shading color for sick
hours used. At the end of the row I have a column for each total, but I want
it added automatically. How can I set up a formula that will use the shading
color as part of the criteri? I've tried using SUMIF but I don't think I'm
using the criteria correctly. Is there a specific word to use for shading
(such as bgcolor or colorindex)?