It's also a matter of the local air pollution profile. Locally, copper roofs turn black. Shocks the heck out of people who put one on without bothering to look at the others in the area. I suppose you can probably apply artificial patinating chemicals (which would also be the solution for your sea monster, especially if it's inside). Outside I expect the normal rain chemistry would revert to black, here, short of patinating and then sealing with acrylic or the like.