Conditional Formatting to ignore blank cells 2003

I am sure this has been asked but I cannot find a reply that suits my simple requirement.

I have a sheet that collates % scores over a 12 month period. I can apply conditional formatting easy enough colouring the cells red, amber or green based on a set criteria. however, as there are only 3 rules in 2003 i cannot get it to ignore the cells not yet filled in and as a result the remaining sheet is red?

How can i apply a fourth rule or am i looking at using more complex formula?
Please help

Many thanks
Colonelkaye