As an airmail collector, I don't know anything about that stamp. But I do recognize the "corner card" -- Colman was a well known Washington D.C. philatelist and dealer. I have two or three of his C1-C6 airmail covers. Nice find.
txstamp, After I get a cert. on it I'll send a copy of the cert. and cover to Scott. It'll be the 5th. new W/F EDU I've sent into them. I'll also copy Richard Frajola to up-date the Berkun-Siskin EDU data base that he maintains on his site.