What is the significance of "blue paper"? In the movie "Gangs of New York", when Bill the Butcher in his "Fear" monologue speaks about Priest Vallon, he states that he, "… cut out the eye that looked away. Sent it wrapped to him in blue paper…"
Bill the Butcher wasn't called that just because of his ruthless demeanor and murderous tendencies. He was also a literal butcher.
Butcher Paper has long been used by butchers to wrap meat and other animal parts. Given the context of the speech, he likely wrapped the eye in butcher paper because he had a lot of it just laying around for his business. It probably also served as a thinly veiled threat to Priest Vallon that this low-life butcher he just spared was going to kill him which is ultimately what happened.
I found this in Lexico, which is powered by the Oxford Dictionary:
Definition of blue paper in English:
blue paper NOUN
Blue-coloured paper, typically used for packaging commercial goods, especially sugar; a sheet of this (now chiefly historical).
A light-sensitive paper used for copying maps and plans, typically made by treating the paper with potassium ferricyanide and ferric ammonium citrate; compare "cyanotype"(now rare).
We can reason out #2, and deduce he is talking about a commercial packaging paper based on the content. It's merely a colorful, descriptive way of saying he wrapped it up in packing paper.