Basically QTC is a material the exploits a phenomenon in quantum-electrical properties that electrons will always conduct in materials even when resistance is extreme.
just play around with the material. You'll need something like a diode ladder to drop a specific amount of voltage at a consistent rate.
hook each output of the diode to a pic I/O pin and program it to say if:
pin2 is
high; pin3 is low; pin is low; you want green
pin2 is
high; pin3 is
high; pin is low; you want yellow
pin2 is
high; pin3 is
high; pin is
high; you want red
edit: forgot to mention that diodes are like resistors that turn on when 0.6v to 0.7v is applied to the cathode.
diodes will always
drop approximately 0.6 or 0.7 just like a resistor.