[Penthode]

I suppose the question is what is the utility of the color killer these days?

The color killer was useful when broadcasters were obliged to remove the color burst on black and white broadcasts. With no one looking after our interest switching off the burst, the circuit has no longer any practical utility.

Or does it?

I have a video switcher before my RF modulator that switches the DVD player outputs between the composite color signal with burst and the Y or monochrome signal output which does not contain the burst. Besides removing the interleaved chroma in the luma thus improving the monochrome reproduction, it also drops the burst which provides the basis to test the effective operation of the color killer circuit.