I looked into it, too, thinking the same thing: conjugated benzene rings must be the photon-wavelength-changing system. Apparently not, regardless of what we have both learned about chromophores. Look at biphenyl (phenylbenzene), which is the conjugated benzene-benzene system in CBN:
On the other hand, lecithin specifically has very little conjugation, and I am not sure of it’s mode of oxidation in air, but I have seen various lecithins in non-polar carriers like oil turn brownish red from a pale gold color over time in air.
Now, I know that cannabis phosphatides are likely present in different ratios than those in soy, for example, and by “lecithin” I mean “phosphatides” in general; I just use the word lecithin because people are more familiar with it and hopefully its antioxidant properties.
I can only guess, for now, what moieties and whole molecules of phosphatidylcholine and other phosphatides are present in distillates of cannabinoids, but I do believe they are there, since citric, phosphoric, oxalic acids, and degumming enzymes all seem to have a precipitative effect on some compounds in solutions of distillate, indicating the presence of phosphatides. Also, performing a thorough degumming sometimes rids the distillate of whatever is turning red.
That said, I also think there are other compounds at work in the discoloration of distillate, such as anthocyanins, or something like them. I am less certain about this than I am about phosphatide moieties, but both are still unknowns until we can get more thorough testing done on our products.