Just thinking about old-school pigments. A light bluish/greenish pigment made in large quantities at the turn of the 20th century was almost certainly derived from copper. Wikipedia explains the related minerals formed and the minor differences in chemistry that shed a bit of light on why Bianchi Celeste may be very difficult to match: Basic Copper Carbonate.

In a nutshell, aqueous copper sulfate produces a blue mineral (azurite) and a green mineral (malachite) when mixed with a sodium carbonate solution, which is the common method of producing the pigment.