Reporting Services Indicators

Hi,

I'm using reporting services to do my indicators, but I need solve a problem.

Well, I have one column which there are variables (values) of previous months and next months. I would like make comparison (figure below) like rule:

If last.value > previous.value then "green"
If last.value >= previous.value then "yellow"

if last.value < previous.value the "red"

Thank you very much !