Circuit idea to use RGB LED for power level

Has anyone seen a circuit that will take a linear or audio taper pot input and drive an RGB LED in such a way that as you increase the level ( volume in audio application ) the LED can be driven from green through the spectrum to Red or Purple etc. at maximum level?

This would be great for custom audio using a lighted volume knob on stereo where the color of the knob changes with the volume level.

With a liner pot it could be added to a nice adjustable power supply to indicate the range of voltage along with a digital readout of the actual voltage. Just for appearance of course.