Copper

Deep blue is one of the hardest colors in Fireworks. Blue usually comes from Copper compounds, but if the flame gets too hot, the copper-chloride emitters break down and the blue washes out. Pyrotechnicians must make an explosion burn “not too hot.”

The Statue of Liberty wasn't always green — it began shiny brown. Its skin is copper, so in 1886 it gleamed a coppery hue. Sea air, salt and pollution oxidized it into a blue-green patina, complete by about 1920. The patina isn't damage; it shields the metal.

The Octopus's blood is blue, not red. Human blood is red because the iron-based protein Hemoglobin carries its oxygen; in octopuses that job falls to Hemocyanin, a Copper-based protein. Hemocyanin turns blue when it binds oxygen, and carries it better in the cold, low-oxygen sea.