Have you tried Virginia Mist/Jet Mist? It has a pattern to it sort of like soapstone and yet is granite.
If you want to try marble but are afraid of the white, try Bardiglio. It is a gray with lots of black and white in it. It is supposed to be easier to keep looking good than the whiter marbles.
I'd also consider a nice wood countertop. That is a classic pairing with the colors you have and since your cabs will be painted, won't clash with other woods used.

Have you considered quartz?

If you like Black Impala you might like Zodiaq Storm Gray or Mystic Black, neither of which match the Impala, but kind of bracket it.

You might also look at Silestone Ebony Pearl or Zirconium, which seems to look different in a bigger sample than the smaller sample.

Also Caesarstone Smoky Ash.

Cambria Waterford, Parys, & Minera

These are not any of the whites, just grey blacks, some with metallic or iridescent inclusions

How big is the island?
Maybe you could use an remnant from a local granite yard.
There are many granites that are marked down becasue the
pieces can not be used on a large island or run of
counter. Remnants tend to be a little cheaper.

And if Granite is still to high maybe a type of wood
counter. Sometimes wood can be expensive but again this
is something you may be able to do yourself.

Another idea would be tile. A DIY project of granite
or even marble tile.

Formica or Wilsonart or even Slate or Limestone might
be an idea to work with.

Here is your corian color, maybe one of the granite
types below might match nicely. (I am a huge fan of Jet
Mist so I can help but agree this would be beautiful)

Mont Blanc Corian

Juperana Persia (A remnant will be cheaper)

Solarius

Vermont Slate

Sandstone Tile

Granite Tile

Wood

Kodiak Granite (this might be beautiful with Mont Blanc)

Ubatuba granite (this is one of the less expensive granites)

Yellow River

Verde Butterfly

Formica is another inexpensive option. (Basalt Slate color)
{{!gwi}}

Jet Mist (my granite counter, I love it)