One's own skin. "in the gonk" (naked). My father (1923-2005) used this phrase in our childhood. His father was in the British Army (Royal Engineers) in WW I, so the army slang "gonk bag" for sleeping bag, is consistent.
Touchstone phrase for situation when one person in a group suddenly notices something that the group has been focused on all along.
Origin: During a long street discussion of a massive fire in downtown Boston in the 1960s, another bystander suddenly said "Hey, look at that purple smoke!"
The group broke up laughing and repeating "purple smoke!". As isolated as the incident may have seemed, I have encountered the same phrase and meaning more than once years later as far away as California.