It seems to me that one of the problems with using the cameras was the varying lighting conditions between arenas. Green was not always green and while the calibration numbers might have helped, I think there is a better way.
What about using LEDs (which have a very well defined spectrum) to illuminate a diffusing panel? This would create a significant area of a well defined color that could be detected. The LEDs can be run off batteries and with proper battery pack design they could easily last at least all day without replacement or recharging.
If you really want to get fancy put a polarizing filter on the diffuser and on the camera to reduce the chance of reflections being interpreted as real signals.
I feel this would make “homing” tasks easier by eliminating much potential confusion.
Just a thought
ChrisH