I think this is where I'd give up and get multicolored wallpaper to tie everything together. ;-) As a color choice, how would a very pale to medium light yellow look? I don't recommend Wal-Mart paint, but they do have a yellow called "Vanilla Creme" and another called "Chanterelle" on card #322. I had them color matched at another store with better quality paint. I think they nice shades of yellow. They might work with the grey and black and add a little sunshine at the same time.

The best small bathrooms & powder rooms I've seen are the ones in which everything really ties together, no quirky odd elements or tangents, & it seems like you can "get away with" more in a small space than in a big one. You can be more starkly modern, more decadently Deco, more specialized & individual. You can put down a floor that looks like water (don't know how that's done, but it's cool), you can use a bright orange 70's theme, things you'd never do in a bigger space. I saw one below-the-stairs powder room that was done in a Victorian theme, very busy wallpaper in warm gold/brown/burgundy tones, dark hardware, dark cabinetry, etc. It was like a perfect little gem. & it wasn't exhausting to the eye because of course nobody spent much time there.

Don't be afraid to go dark in small places. Dark works amazingly well in small places-imagine huge room that you use all the time painted dark..not for the weak nerves. While in smaller places, especially ones where you spend just so and so amount of time, dark is enveloping, cozy and calming actually-or elegant and striking, depending on the direction you take. Don't be afraid of contrast with white fixtures. Dark loves some white, and light touches, shiny surfaces like in your mirrors or lighting fixtures, metal (fixtures yet again, and picture frames for example)..it can become easily one of your favorite places in the house if you treat it like a little room. Go with one of the colors in your tile(it already has many, so I'd keep to one of them)...if your ceiling is standard-tint it with a wall color, in proportion more then usual, so it won't feel like a box with a white lid (usual proportion is around 5-10%..that' what good painters do when painting rooms. In rooms with standard ceilings and dark walls you might want to go as high as 50%..check it all of course beforehand, play with the proportion. every room has its own light thus its own rules. it won't make a room darker; it will create the illusion of a higher ceiling though, and prevent the white lid effect). If the ceiling is higher, then you have less to worry. But I'd tint the ceiling some anyway. Also, crown molding helps a lot in these cases..the line where walls and ceilings meet seems softer and somehow more pleasing to the eye. If you leave your paint semi gloss-it will also create the illusion of a room less dark, because the sheen is so reflective. Add art you love, and generally have fun with it-a rug in a richer tome/interesting pattern, a shower curtain that picks up the color, even just in a tiny detail, a little plant, an interesting mug instead of a regular toothbrush holder..you won't pay attention to the tiles you're not a fan of, because the bathroom will have other things you love, in abundance. Disclaimer: everything I suggest here, I went through myself..))

I am not a professional, so full disclosure there, but I understand your frustration and I am in a similar situation. Its always hard to see color in photos but it looks like you also painted your wood door frame in the same color as the cabinets? An easy solution would be to repaint the cabinet white and door trim white, leave the grey on the walls. What is the trim color in your hallway, flooring color? These items also figure in to the colors of you bath. Its nice to pull in the color from the outside flooring just a tad or to have something on the walls, floor or counter that pulls it all together.