IKO are the worst quality shingles on the market right next to Tamko. They're thin, have no impact resistance and have had multiple class action suits as well as individual suits against their products. Darkest black shingle is Owens Corning Onyx Black. GAF does not make a color called "black" but have "charcoal" which is their black shingle.

We are doing the same - GAF Timberline HD in Charcoal with black standing seam metal on the porches and roof/cornice returns. I recommend you open up one of the shingle bundles and pull a few of them out to get a feel for how it really looks. Our actual shingles have much more gray in them which is what we wanted. The demo piece on display in the store was completely black and not indicative of the actual product at all. Seeing the actual shingles will help you better pick that metal.

They could be GAF, sure. They could also be Tamko or Owens Corning or CertainTeed. All the major roofing shingle manufacturers make versions of the same thing.

Thanks for responding, @Beverly. It turns out, 99% of shingle colors are unavailable right now! (That's 2020 for ya). We had to switch from GAF to Tamko, and went with one of their grays (similar to the gray you highlighted above). Hoping we love it!