Try a sample of PPG Greyhound. Samplize.com. This paint color has some brown in it. Imo, any paint that just reads cool grey is going to emphasize the violet tones in the tile that you say you don’t want. Plus, it will leave your space with a cool/cold type of feel.

You need a paint that leans warmer, imo.

This is the PPG Greyhound in your room.

How you reduce the presence of a color is to introduce that color in a much stronger form. The eyes will see the stronger color, and the paler color's undertones will disappear. The eye is fooled.

That's a beautiful shower stall. Very nice.

The safest and easiest bet is to choose one of the colors from the tile, so as to blend the tile color seamlessly throughout the space.

The blue accent tile will become just that, an accent color against the rest of the room. Use accessories in the color of the blue.

I would try Behr Day Spa... a fresher white with a hint of blue gray.

How do you feel about black accents? Paint your accent wall opposite the tile wall Tricon Black from Sherwin Williams? Maybe use black faucets, shower head, etc?

I adore BeverlyFLADeziner's suggestion of a compatible DARK color. It really pulls your excellent tile selections together in a beautiful, dramatic way. You see the room, not separate elements. Don't go with the safe, boring, almost-there colors!

Spend some time on Maria Killam's website before you commit. She discusses undertones, color rescues, when to use black hardware, timeless design, etc. and her blogs are spot on.

https://mariakillam.com/three-different-undertones/

If you want to stay with a lighter color, look at BM Paper White. It is a blue-gray off white that looks different under different lighting conditions, so I can't guarantee it will work in your room, but I used it in my laundry room in my last house and loved it. It gets along with other colors well.

Beautiful choices so far. I agree that you probably want to put a darker color on or something in the same family as the feature fish-scale wall. There are various online color visualizer tools. I used the Behr one and imo found that something such as Tidal (M510-6) might be appropriate.

Or be bold and paint that wall a blue closer t te fishscale - and have the onyx be the accent!

Both tiles are cool temperature. Stop with any paint with a warm tone. Don't muddy it up either. I'd match the fish scale for paint: )

Beverly up above gave it to you, and call it the keys to the casino! Right here below. Cohesive, bold and shows off BOTH tiles . Lordy.....we haven't seen enough gray walls? I think we have. Add some smashing art, to the painted wall.

Gray Owl is GREEN, no matter what you pair it with.

Meg, do you get a lot of natural light in your bathroom? If so, from which direction? I would like to see a photo of the complete wall you want to paint. Perhaps a wide angle photo to give the bigger picture would also be helpful.

I love the onyx tile. Would you be willing to share the manufacturer 's name and color name?

Meg, I found a nice article for you at HR, Hampton Redesign. It is about finding the correct neutral color for bathrooms.

Exactly How to Choose a Neutral Bathroom Paint Color - Hampton Redesign

Meg, if you look at the medium blue shower wall in this link you will see that the designer carried the pattern down to the floor. Without seeing the rest of your bathroom, it is difficult to make a suggestion. However, you clearly like the blue so try to carry some of the fish scale blues out to the room in floor rugs and art on the walls. See if you can find a paint that will enhance the blue scales and blend nicely with the purple tones. I really like the colors and think you would be bored by it if the tiles were just veined with blue. You have a great backbone here and I look forward to seeing your finished project. Please keep us updated.

MWAI - Architects and Interior Designers, London

Don’t go warmer, go cooler! IMO, since that one wall is so dark, I’d stick with a lighter wall color.

Thanks, everyone, for the great suggestions and very helpful renders. Tile and other installation work has been ongoing so I’m including a couple more photos here. In answer to cornflower crayon’s question, there are 2 windows, one north and one west-facing. The onyx tile (12x24 Athena Blanc polished) is also on the floor of the bathroom. I like the dark suggestions, but my wife is not on board for that. I have a sample of BM shoreline I may try, and the basement is Stonington gray, which may be too icy here. Appreciate the input and welcome other questions/suggestions!

Well, that is even more attractive than I thought!

It appears that the north window is opposite the entryway. Is that correct?

Also the tub and vanity top are the same white, with a cool tone or yellow tone?

The balance of the 2 tiles throughout the room is very cool.

I will be toying with this tonight.

Thank you for sharing this with us. It helps all of us learn. Peace.

https://assets.wfcdn.com/im/16524710/resize-h445^compr-r85/6570/65709180/Metro+16"+x+16"+Ceramic+Field+Tile+in+Rust/Orange.jpg

I would love to see a rust, copper, orange added to this color palette

Add green plant later or towels & rug.

What is the vanity finish? And the floor? What is the plan for base and window trim finish? The style of the trim around the window is too traditional with your bathroom design.