Manage Pie Chart Color Choices

I am creating a Pie Chart for a dashboard.  Lets say the pieces are based on a field called Area.  The most values I can have are six (Americas, China, Europe etc.).  Sometimes the pie may only have two pieces, sometimes 3, sometimes six based on the other chart criteria.  Can I control the pie chart colors such that when Americas is on the chart it is always blue, China is always yellow, Europe always green as an example.  Basically I want to assign a color to each region and only have it used if that Area appears.  I've tried