Screen Shot 2019 01 12 At 10.30.23 AM[1] image and description

Thereby, you should probably go for minimalistic wall/floor/ceiling-mounted lights. They won’t abstract any design details, and won’t sophisticate the style too much as well, while giving off just enough light:

• For example, you can find a strong rectangular light that can be plainly mounted into the wall. A good place for it would be aside the mirror, especially if it has the same height as it. It will throw a load of light on a vanity (which would better be white), and walls, which would reflect that ligh across the whole room.
• Another way of mounting the lights would be by hiding the light source behind something. Be it just furniture or, perhaps, rugs, by hiding the lighting behind them you will create a strong feeling of spaciousness, everything wouldn’t look as artificial and still be very bright.

Warning! It is not recommended to mount the light into the tiles, as that may cause it to beam the whole room from bottom to the top, obstructing your view etc.

Conclusion

For the conclusion remember, that designing a grey bathroom is mostly about hiding everything that might look bad/overly complicated, and leaving everything else. Basically, play a game of hide-and-seek with the lights. Thankfully, due to grey being the color it is, as stated above, you don’t need to mount too many lights either.