Hi again - I see what Calvin's saying about leaden - it may not sing as well. But I know what you are talking about with that lead-colored sky. Icy wouldn't convey the same image and the lead contrasts with gold in the previous sentence. This is a very tiny change that might sing better but may not even sound different:

"As if the sky resembled melted gold
Instead of lead in wet December cold"

I like it how you have it just fine though. Anne


Anne M-W