The PAL Game Boy Player add-on for the Game Cube seems to output "whiter than white" levels for the composite output. I have tried this across multiple systems, cables, TV's etc, with the same result - completely washed out colours, with detail missing. One way of getting around this is to split the signal before it hits the display or capture device.
The first image below is the signal without being split, the second is the signal with a split going to a TV. The difference is huge.