I don't think that it would be overkill to paint the beadboard and vanity both white, but the top half of the walls definitely can't be white. I would suggest you paint the upper part of the wall a lighter shade of grey or a grey-blue such as 'silverscreen' which I think has a light but neutral hue.

I'm pasting a link to a page that shows the color. Let me know what you think

Here is a link that might be useful: Involving Color -- Silverscreen Color

Scary Cary(cute name!) I had not considered a blue-grey color but I really like the look. I have a hard time making color decisions so your input helps a lot. Thank you.

Definitely not black - that would be too dark with the black countertop. I see lots of white vanities with white beadboard and it looks fresh and clean.

Why does the vanity need to be either white or black? It would certainly need to play nicely with the upper half of the walls -- maybe just a lighter or darker shade of the same color? Or find two colors you love that play well together.

Sweeby adds good insight into the process...why black or white? Though I understand that B or W might be the answer to your room question.

Check out houzz.com for a lot of pics. Just type in a search to help narrow down the ideas. There are millions of images.

Personally, I would paint it white or gray. I think black wouldn't showcase the granite well enough.