Changing color of Pivot Table cell based on Expression

[#1]

Hi all,

I have a Pivot Table that sums sales for each product during the last full 365 days.

My Dimensions are:

Product Class  (like toys, shirts, pants)

Product Name (like race car, tanktop, grungy jeans)

CalendarMonthYear May-2013, June-2013 .. . .  Apr - 2014)

My Expression is:

SUM({<Product_ProductName = >}Order_Counter)

What I want to do is change the background color of each sell to red if this months sales are lower than last months sales and green if the are greater.

Thank you all for looking and your help.