I use a good trick. A change the formula to:

=IF(G2="",0,IF(M2="",0,M2-D2))

Get the result. But a problem. Excel was displaying the 0. Then I uncheck
the "Zero Values" option from Tools - Options - View tab.

Hope this helps you too. Let us know!

"SD" wrote:

I want to use three colours to highlight a spreadsheet, red for numbers less
than -1, amber for number between -1 and 0, and green for numbers greater
than 0 which I can do no problem. Each cell that I am colour formatting has
the formula (or similar):
=IF(G2="","",IF(M2="","",M2-G2))

However the blank cells are also being coloured in green when I want them to
remain white. Any ideas?