Blue tinted spectacles were available for the very rich from the early 18th Century. It was thought the blue glass could be 'ground' more finely than the clear stuff. On the website Chirurgeon's Apprentice, one can see a photo of the very type of thing. It says there that Samuel Pepys wrote about them as being prescribed for syphilis sufferers, who found bright light painful. If this was generally known (although the site has doubts on this) then maybe the Little Beggarman was insinuating that he too was a sufferer, and would probably wink hugely when he sang this line! Anyway, such specs would cost a fortune, so the chap was listing fancy stuff he proposed to wear to seduce the flaxen-haired lass. Flaxen-haired is still a current expression for a blond person.