If you have a cable that has one connector on one end, and three on the other; then it's the wrong cable.

The cable you want is properly titled an "RCA connector to RCA connector" cable. All RCA connector cables carry only one single signal per connector. Composite video, monophonic audio (hence the use of two for stereo,) etc.

It really doesn't matter what color the ends are, those are just meant for convenience in connecting the two ends. I have a three-connector cable that has no color coding. It's a pain to keep straight, but it works just fine. It's just common convention to use white for mono sound or the left channel of stereo, red for the right channel of stereo, and yellow for composite video. It honestly doesn't matter. Right now, my IIc is using a red/white pair cable, but only using one of the two plugs. (I believe I'm using the white, but I don't recall off the top of my head.)