I'm going to go ahead and call this a duochrome... ish. Empire State Blue is not entirely blue. It seems to shift from green (it's got gold shimmer in it that makes it look green) to blue but it's not so perfectly duochrome that the shift is always there.
I tried to coax this effect out by moving my fingers around as I took the pics and I think I sort of managed it. However, whether it's a duochrome or not it is absolutely beautiful. The blue and gold shimmer is so stark and present that it always gives it an extra kick wherever it is. It takes around four coats but it's so easy to apply it doesn't feel like extra work.