To look blue; to be confounded, terrified, or disappointed. Blue as a razor; perhaps, blue as azure.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Blubber Cheeks * Blue BoarNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes