D all of the above and E none of the above....
Who says that AGs are gray? We humans don't really know what color they are since they see each other quite differently...
See the quote from this url for instance: http://www.bio.bris.ac.uk/research/behavior/icc_vis.htm
"Colour Vision in Birds
Bird colour vision differs from that of humans in two main ways. First, birds can see ultraviolet light. It appears that UV vision is a general property of diurnal birds, having been found in over 35 species using a combination of microspectrophotometry, electrophysiology, and behavioural methods. So, are birds like bees? Bees, like humans, have three receptor types, although unlike humans they are sensitive to ultraviolet light, with loss of sensitivity at the red end of the spectrum. This spectral range is achieved by having a cone type that is sensitive to UV wavelengths, and two that are sensitive to "human visible" wavelengths. Remember, because 'colour' is the result of differences in output of receptor types, this means that bees do not simply see additional 'UV colours', they will perceive even human-visible spectra in different hues to those which humans experience. Fortunately, as any nature film crew knows, we can gain an insight to the bee colour world by converting the blue, red and green channels of a video camera into UV, blue and green channels. Bees are trichromatic, like humans, so the three dimensions of bee colour can be mapped onto the three dimensions of human colour. With birds, and indeed many other non-mammalian vertebrates, life is not so simple. As well as seeing very well in the ultraviolet, all bird species that have been studied have at least four types of cone. They have four, not three, dimensional colour vision. Recent studies have confirmed tetra-chromacy in some fish and turtles, so perhaps we should not be surprised about this. It is mammals, including humans, that have poor colour vision! Whilst UV reception increases the range of wavelengths over which birds can see, increased dimensionality produces a qualitative change in the nature of colour perception that probably cannot be translated into human experience. Bird colours are not simply refinements of the hues that humans, or bees, see, these are hues unknown to any trichromat."
So we really don't have a clue, do we?
Cheers,
Renate