I thought reflected moonlight was polerised,(sp), I would think this would make the formation of a luner rainbow very rare, ie the normal colour spectrum does not show in moonlight.
I have seen a ring around the moon,on a few occasions,the colours are not as bright as your terrestrial rainbow but they are there.
I understand these are caused by ice crystals high in the earths atmosphere.
A astronomical phenomenon I have seen in print a few times is that in really dark conditions the planet Venus can cast a shadow.
I always used to look out for that when venus was at maximun elongation, never seen it though.
Also although I have seen hundreds of sunrises and sunsets at sea, I have never witnessed the green flash.
Mebee its just me
PS sorry POD as per usual I did not read your post correctly, I suppose a mono chrome rainbow is possible with polerised light