I just did a "Basic Search" of the USPTO using their "TESS" system, and confirmed the above statement. Colby is nowhere to be found in anything based on "IBOOK" ("IBOOKS", etc.)
Colby's suit is not going to get far. In order for a trademark to be defensible, it should be registered. Seems awfully silly of Colby not think of that.
"BZZZZTTT!! Sorry, play again."
Since Colby bought the company from out of bankruptcy that was caused by death there might have been incomplete transfers. I’m sure iBooks was registered at some point, I own books published by them, the question is was that registration transferred.