The reason you get a black and white signal is because your Super Video (s-video) output sends 2 colour groups to your TV, 1 for colour information, the other for brightness and lighting information. If your TV is not designed to receive a s-video source it may not pick up the colour information hence the black and white image. I had the same problem when trying to plug my laptop into my parents TV.
What you need to do is change your graphics card output mode to composite (RCA) If you can't change these manually and your not confident with cutting up wires and don't want to risk damaging your hardware. I would recommend buying a converter, these can be found on-line for a few pounds. Your graphics will then automatically change to a composite output and give you full colour.