I think he understands physics better than that. I think a photon with the properties Shrike describes will produce 'green' light independent of the medium through which that photon travels.
Perhaps he knows more than I, though. It's not really my field. Roland's observations about optical illusions aren't really relevant.
If Jonte means something like "Sunlight loses red wavelengths and shifts to blue as you get deeper in the ocean", then that has nothing to do with light itself changing, and instead has to do with the water and particulates filtering out some colors while others continue on. 'Red' and 'Blue' don't change - blue pierces the water better and red is blocked. "What is red" does NOT depend on that medium.
If he means that an observer who is travelling away from the light source at relativistic speeds may see a shift in color, that again has nothing to do with the medium.