I'm recalling an article in Scientific American some decades ago addressing the Green Flash mystery of being frequently observed by eyes but never captured on film - its a biological phenomenon produced by prolonged staring into the sun as it nearly disappears beyond the horizon. The light reaching the eyes is mostly red due to atmospheric refraction and causes saturation and reduces sensitivity of red-sensitive segments of photoreceptor cones in the retina. As the intensity drops quickly the desensitized red-receiver portions will produce a lower relative neural response receivers for other color , thus altering the neural color balance and creating a perception of green color. This may be similar to the momentary blindness we experience when entering from a brightly-lit room into a dimly lit one - except that it has a bias for red color illumination.
Another possible mechanism hinted at in Wikipedia is light frequency doubling that occurs in the retina from invisible incident solar radiance at near-infrared wavelengths of, say 1.06 microns, due interaction with the nonlinear response of the retinal photoreceptors, resulting in wavelengths of 0.53 microns, smack in the visible green band. That invisible radiance penetrates through the atmosphere (if clear) and propagates through the eye to the retina but our photoreceptors are insensitive to it - however they will react to a frequency-doubling effect locally converting it to green light.