Do you know the old joke, “What colour was Napoleon’s white horse?” Well I have another one for you: “What colour was Napoleon’s greyhound?”.
Not sure? You may consult the Official Greyhound Colour Chart:
Apparently < a first element cognate with Old Icelandic grey bitch (further etymology uncertain: see note below; compare Old Icelandic greyhundr bitch) + hound n.1, with later assimilation of the first element to grey adj. by folk-etymological association and by analogy with other animal names in grey adj.Further etymology: A derivation of Old Icelandic grey from the Germanic base of grey adj. has sometimes been suggested, but is very doubtful, not least on semantic grounds.
Folk etymologies based on reanalysis are often interesting because they reveal a fact about human perceptions. The word ‘acorn’, for instance, was perceived for a long time to derive from ‘oak’+’corn’ (or ‘kernel), since acorns are the fruit of the oak, which is true enough. [But ‘acorn’ is not oak-corn; it’s related to ‘acre’ — the open land where acorns might be gathered].
What’s especially interesting about this folk etymology is that greyhounds aren’t grey! Probably never have been. So the reanalysis that makes morphological sense (‘grey-‘ not suggesting anything better than ‘grey, adj.’) makes no real world sense at all.