Can Numbers do conditional coloring of a cell based on a rule? I have a spreadsheet of open projects with payments for each milestone. 
Right now I set a cell to red if the client still owes, green if the client paid, and no fill if we havent reached the milestone yet. What I would like to do is get a sum on all red cells and another sum on all green cells. My hope is to make it easy to see how much money has been paid and how much is owed.
Here's a better option:


Add an 'Account Status' column
Select the entire column and set the cell format to [Pop-Up Menu] with options for 'Unfinished', 'Paid', '30 Days', '60 Days', '90+ Days' (or whatever options you want)
Select the entire column and set some conditional rules to color the cell according to the text in the cell (e.g. a green for [Text Is 'Paid'], a yellow for [Text Is '30 Days'], etc.)
Add some summary cells with COUNTIF formulas for each of your Pop-Up menu options ([=COUNTIF(Account Status,"Paid")], [=COUNTIF(Account Status,"30 Days")], etc.)


Note that this will color ONLY the cells in the 'Account Status' column. There are some tricks to color the entire row, but this should be enough to catch your eye.

You can also use AppleScript if you need more complex summaries, but scripts cannot run automatically, where conditional rules do.