It's a sequential colour camera, each field is red, green or blue filtered (using a spinning colour wheel), and they're processed back on earth to recombine them into a colour TV picture. Doesn't work that well with fast motion, as there's too much movement between the red, green, and blue images, hence the rainbowing. They were of course bandwidth limited so conventional NTSC might be an issue. Also a normal colour TV camera at the time used three (or four) image tubes, rather than the one in the Apollo cameras, which would have added size and weight (this is before things like CCDs were practical).