Green

The green in the Italian flag came from a newspaper error. During the French Revolution, an Italian paper reported the French tricolors blue as green. Revolutionaries adopted it, and by the time the mistake was found, green had gained its own meaning.

Hulk from Marvel Comics was originally gray. Stan Lee chose gray as a scary color unrelated to any ethnicity, but a CMYK printing error turned Hulk green in the first comic issue. Lee liked the result and made green Hulks official color.

Paris Green, an 18th-century pigment, became popular in Europe. It even repelled insects when painted on walls. But its ingredient, arsenic, killed many before it was banned. The convention of depicting poison as green may originate from this deadly pigment.