Consistent Colors for Pivot Charts

Hello,

I am creating a pivot chart and I have a drop down boxes on the top and on the right (I'm sorry, I don't know the terminology). Anyway, let's say that I have 3 items showing in the drop down box on the right. If I make each item a customer color (by double clicking the the little color box to the left of each item listed under the drop down), the colors are reflected in the chart. However, as soon as I try to display new data, excel automatically diffaults to the basic colors and not the colors that I chose. Thus, the chart that originally looked great now looks different and I have to go in and again double click the little color boxes to stay consistent. How can I keep these colors constant? In other words, how can I associate a set color with items in the right most drop down box of a pivot table?

thank you so much, I just can't figure this one out!