Here are 3 different color options for GrayFin. I've also worked a bit to clarify the "F" in fin to make it read more like a fin but still keeping with the square modern feel of the type. One thing you'll notice, is we can't really make the "F" look completely capitalized simply because we are emphasizing the arc, which is not in a capital F. I've adjusted the proportions of the F to try to communicate being a capital version as much as I can. Also, there are also a couple of ways we can use the "fin/f" in an icon form.
As always, let us know what you think!