Colorimetric separation is a professional problem in TV transmission technology,
The video signal of TV is composed of red, green and blue chrominance signals, but in TV transmission, a separate channel should be more than 6M and the bandwidth, the three signals should be used at least 18M bandwidth, so it can't be transmitted directly. The signals must be combined.
Based on the discovery of the signal, although the bandwidth is very, but not all the frequencies are occupied. This makes it convenient to insert the signal in the gap and transmit it.
The PAL television signal is transmitted by a luminance signal and two chrominance (red-bright, blue-bright) signals. The luminance signal modulates the main frequency directly, and the two chrominance signals are orthogonally modulated with a 4.48M chrominance subcarrier and then modulated with the main frequency. Just the free positions in the bandwidth are utilized. The chrominance subcarrier and luminance signals are then interleaved like two opposing combs.
The receiver must then separate the chrominance subcarrier from the luminance signal, which is the chrominance separation circuit. The chrominance separation circuit includes: a delay line, a demodulator, an adder, and a subtractor.
Because the two signals are interleaved with each other like a comb, they must be separated with a filter that has frequency characteristics like a comb. The ultrasonic delay line has such a characteristic because whenever the line length is an integer multiple of the half wavelength, it happens to produce a superposition or cancellation, and its frequency characteristics are shaped like a comb, so the delay line filter is also called a comb filter. With this filter, the chrominance subcarrier is separated from the luminance signal.
The demodulator is what demodulates the two chrominance signals from the subcarrier.
Adder: The red-bright and blue-bright signals are added to the luminance signal to get the red and blue signals.
Subtractor: obviously, bright-red-blue = green. This reduces the red, green and blue signals.
Designing such a circuit is called ultrasonic delay line based chromatic separation circuit design.
This is a well-established circuit in TV (or PAL disk drive) technology, so look for a transistorized TV circuit schematic (I don't have one on hand right now). Most DVD players use large-scale integrated circuits, which don't help much in learning the principles.