Changing chart color based on number entered
 

I am trying to creat a simple pie chart with two numbers. I need the chart
colors to reflect the number. Example: 0-50 = red; 50-100 = blue. If one
week the first number is 37, the left side of the chart would be red. The
next week the number could be 89, so the left side would need to be blue.

Any ideas?