I'd go for a black wall-mounted vanity and a solid white top.

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I would never do hex tiles for shower walls , I actually dislike them even on floors . But now you have them i think a color from the tile for the vanity so black is the obvious choice and a simple white top and integrated backsplash .

Two pros give the same response, go with the first one.
Good luck with your project!

I was thinking the same, follow the color placement in the shower - black vanity with white top. But I would look at tops with a subtle grey veining to match that on the shower tiles.