All excellent posts.
My 2 cents - in the context of this being the Dzogchen thread.
For me, the 5 lights are really just a way to speak of how physical reality - the elements - can be represented in a useful way so that there is a handle to use when working in the physical dimension. Name and form, form and name - you (I) really can't say which came first, but in the conventional reality of the physical dimension, these serve a useful function.
In Dzogchen, in the spiritual dimension, all 5 lights are really contained, as an unnamed awareness, in the clear light of "pure from the beginning" AND co-emergent "spontaneously arising" awareness / consciousness of infinite possibilities.
In this dimension, the 5 lights are not defined as any one element, 5 elements or as anything.
In practice, (for example in the sending of light from a white ah in a tigle of 5 colors) the individual colors need not be seen as anything other than a swirl of clear light, which by undefined definition contains the 5 colors and all other intellectual fabrications. It is the dissolving of ordinary consciousnesses (the 5 colors, or differentiated colors) that is set to rest in the undifferentiated clear light consciousness.
It's a kind of value added, equivalancy table, where normal consciousness is informed by certain intellectual understandings (for example - the 5 elements equal the 5 colors of light,) and then --- from this normal consciousness, amazingly, clear light consciousness spontaneously arises.
So perhaps from the point of view of the clear light consciousness, there is no thought, or recognition, of any differentiation of anything, and so perhaps it is not so important what element is represented by which color.
All of which is easy to say and hard to do.
Which is why we seek a Dzogchen Master, take direct introduction, receive transmissions of practices, and then do the practices.
Hope this explains, one answer, as to why air is represented by the colo(u)r green.