Hello, guys!
Here is something interesting (old circuit with new feature):
Big Muff Civil War equipped with bicolor LED for fun.
How does it work? When stompbox is switched on, red LED slowly appears and stays on. When playing, blue LED brightness depends on sound. Full brightness is at 300 mV, and minimum is at 30 mV of output signal. When any sound is strummed and then decays, the colour mixture changes: blue-purple-lylac-mauve-pink-red.
It's very pleasant process, I have to say!
This additional circuit is not much complicated and its current consumption is less than 0,5 mA.
Input impedance of circuit is more than 500 kOhm and it does not affect to sound.
It may be incorporated to any stompbox with ease!
Do you like my idea?
Inside:

Outside view is here:
http://postimg.org/gallery/26kejde4a/