To change the color of the panels, background (coordinate plane), curves, or axes first select the corresponding radio button and then click on a colored box provided. The color for the element you have selected will change accordingly.
If more than one function are being graphed, you can change the color of the graph of an individual function by entering the number representing the function in the text-box next to the curve radio button and then click on a colored box. The Function Grapher Applet then re-draws the graph(s) changing the color of the corresponding curve.
Pressing the Reset Colors button will change the color of the elements to their original state.