Copper turns green as it oxidizes (reacts with oxygen).
Our revels now are ended. These our actors, As I foretold you, were all spirits and Are melted into air, into thin air: And, like the baseless fabric of this vision, The cloud-capp'd towers, the gorgeous palaces, The solemn temples, the great globe itself, Yea, all which it inherit, shall dissolve And, like this insubstantial pageant faded, Leave not a rack behind. We are such stuff As dreams are made on, and our little life Is rounded with a sleep. mycroft16 on Twitter
Brass is an alloy of copper and zinc that looks gold, So the sign may have been brass, if it was a gold color. Both brass and copper get a very nice patina when left in the elements. Brass gets more dark/black than green like copper does. The roofs on main street, on the right side when you enter the park are made of copper and if you look, they have a wonderful green patina.
Disney also oxidizes (a way of getting a patina by using chemicals) lot of their brass railings to make them black, you can tell which railings get touched more because they have been polished by visitors hands. you can really see this in the silly swings area railings. that is all.