How to Change Perspective Icon Color Back to Default?

I created a custom perspective. I tried out some different colors for the icon to see if I liked them, but decided to stick with the default color. Little did I know I had stepped into a trap. Once the icon color is changed it is not possible to go back to the default color since the default color is not one of the custom color selections.

Am I missing something here, or is there a way to do this?