I suspect that Brookfield made this Manhattan insulator... this one is a typical color for a Brookfield, dark aqua with green streaks, and has a mold line across the base. This is a feature that is connected with a certain time frame of Brookfield production (although not unique to them). This picture tries to show it (hopefully). The inside of the base comes to a very sharp edge, which is typical of this mold style. Interestingly, this mold shows evidence of being modified, as it has an "extension" line running horizontal around the insulator just above the base. It's as if an extra piece of metal was bolted on to the mold and then machined to create the part that would form the base.

This makes some sense, as Brookfield won a patent lawsuit against Novelty, and inherited their molds as part of the settlement. It wouldn't take much for Brookfield to determine who the customer for this insulator was, and to offer to continue supplying them... :-)