How about going retro? You already have the flooring for it. Paint the vanity something in a mid-tone color, if that fits your style, paint the walls a light shade or a lighter shade of the vanity, add some decent lighting and retro art, the perfect towels, and you will have a bright and cheerful space even without a window. See Houzz photos under "checkerboard floor" for ideas.

Just about anything can go with your black and white tiles. You can paint the cabinets black, white, or grey. Or you can go with a fun color like bright Aqua? Is there a style you'd like to move towards? Adding a mirror and good lighting will help you forget your lack of windows.

We have a windowless basement bathroom. The floor is med/dark gray, and we kept the walls lt gray. All trim is white. We used accents of Aqua - with a retro vibe. I hung towels in a geometric print of aqua, white and shades of gray.

Thanks for all your advice! It hadn't occurred to me to simply paint the ugly cabinet - I think that I will do that first! Then probably blue-gray walls and lots of bright white. Good ideas!