How does this high pass filter in a mini color organ function?
It's probably best to think of it as a normal differential amplifier, but with a complex impedance on the non-inverting input resistor (R2 in the following diagram):



The derivation of the equation is shown here, but it simplifies down to:



Now replace R2 with the capacitor impedance R2=Xc=1/(2*pi*f*C). We can see that as the frequency increases, this term decreases. This means that the V2 term increases as the frequency decreases, making the output increase and making the circuit act as a high pass filter.