Out of curiousity, the TV you plugged it into, was it a PAL TV? Because i think the IIGS only supports NTSC, and therefore will only display colour of the TV is capable of accepting NTSC signals (some TVs, like our Sanyo allow you to switch between NTSC, PAL and AUTO, but others don't). Check the OSD menu, or failing that, the documentation that came with the telly.