It basically tells you that you can basically tone the "colourness" (i.e. the brightness of the colours) up and down, which was a normal control (like brightness and contrast) back then. This is not about being able to make a red playing field green by some setting on the TV. You just had some potentiometers to play with the pre-amplification of the luminance and colour signals.

What could be in the instructions would an explanation of the games telling you that e.g. the playing field is green and the ball is red or somesuch, then they actually did a (rare) "colour implementation" of the circuit.

If you are interested, there is a number of interesting documentations on this pong chip on the net.