You can filter more than just the color of the light. Look at how TV remote controls work. The transmitter sends data with a specific carrier frequency. The receiver responds only to that frequency, like a radio tuned to only one station.
I guess that you want to use green light for the look. That's probably not going to excite a regular IR receiver properly. If you could use red, then that's probably close enough to infra-red to make it work. But I'm sure that you could find a "remote control" receiver that does respond to green light.
Light-to-frequency converters sound like very old technology. Probably expensive too. Modern IR receivers are available for cents or micro cents.
If it gets really difficult/expensive to detect the green light, then perhaps you can put an IR laser alongside the green one and use that to detect the fingers.