Here is a version...
In this circuit, the 3 way switch is shown in the #1 position. You can elect to have the tone control in or out here. Position #2 uses the tone control. Position #3 eliminates the tone control and places a large cap (your choice of value, probably 0.2mfd) for a "dark" setting.
Simultaneously, the other half of the switch engages or disengages the SPC control, modified as shown. In position #1, the SPC is out of circuit as the output pot is simply disconnected from the device. In positions #2 and #3, the control is reinstated.
The addition resistors are there to prevent noises from occurring as the switch is moved from position to position.
Any questions, just ask.