there is not absolute rule.

this is mine. The shower faucets are the same matte black as the sink faucets. I did really gold looking knobs on this RH vanity so I could tie in the gold mirrors and sconces.

I have 6 diff type of tile in this bathroom (black and white, and marble) I accented w/cobalt blue in the window glass and the sliding doors to the water closet. I can do any of those 4 colors in the towels (gray too)

If you want to see the entire space, click on my name and go to master bath redo.

In my kitchen, I also did black/gold. I dont' care for SS. (I also have a coffee bar w/black/white cement tiles and walnut shelves off to the left of this picture)

If you're doing a powder room, you can go a bit bolder and do whatever you like. I don't have a clue what your style is or what you want things to look like.

The best way to start is with some inspriation photos that match your ideals and style. Then you want to figure out what you flooring material is going to be. My bathroom took me months and months to get all my selections chosen. (my problem is that I like too many diff things and know far too much tile!)

In my small half bath it is all the same. In my master the mirror sconces, mirror, shower head, and towel rack ect are polished nickle. The pulls and faucet are that new gold color.

If you find something you love then make it work.