A soft, warm grey shade would look lovely, and can be as dark or light as you want. A warmer shade will work with the brown stained wood floor, and the grey will complement the black granite. You could have an undertone of green, blue or tan if you didn't want a pure grey. And it would look nice with any silver metal hardware, either polished or satin/brushed, so you could choose pewter, chrome or nickel. It would still work with white trim too.

Really like the counter top combination. To create a finished look (rather than a haphazardly thrown together look), you should probably use the same color on both vertical spaces -- the same color as is between the diamond shapes on the wall.

If you will like to go little different than Indian / traditional one, mint green colour is in trend and goes well with brick colour walls. Looks good if you have white appliances, crockery and some other elements that are visible with it. (Sourced from google images) https://goo.gl/images/Wyu1kR

Hello Abinash, Correct me if I am wrong in my guess that you liked the basin so much that this entire unit was build around it :) that too in the centre of the room. Jokes apart, the base cabinet doesn't provide a few inches gaps to the user for keeping the foot comfortably while using a hand wash. Have you considered the water proofing and maintenance of this unit as what it appears it is wood with laminated top as of now. Do you have a floor plan, as it is a surprising positioning of a hand wash. Thanks, Nitin CORNERSTONE DESIGNS Bangalore