The grey sobriquet wasn't in vogue or part of the parlance in 1947 and her father using it on his deathbed to describe what he saw during the Roswell incident indicates he was influenced by the post-1978 Roswell dialogue of Stan Friedman and other Roswellian investigators.
Authentic memory reconstruction of significant events remain saddled, if not bolluxed by ex eventu input, by the language and milieu of the initial memory recall.
Current terminology used in a past memory recall is a sign of a neurological flaw or a deliberate fabrication. [See "automatic memory" in Psychiatric Dictionary, Fourth Edition, Hinsie/Campbell, Page 461]
Ms. Green either used "the greys" epithet on her own or her father used it after being "indocrinated" by the Roswell tales in situ after 1978.
Either way, the deathbed reconstruction is iffy at best or bogus in fact.