but I like the color May green, it always cheers me up. ;-)
True. A very refreshing color. About 10 years ago I had it as Kiwi Green in the kitchen, my mother as Apple Green.
Since we will have light "wood decor-" tiles everywhere on the floor, free walls for beautiful pictures and space for large plants, a self-built wooden washbasin, I think it will be okay. We will take care of the color design of the non-tiled walls after moving in.
If it is "okay" for you, then do it that way. The bathroom you want should be refreshing and invigorating, at least that’s my understanding, also considering the example picture you posted. I think, at least for me, that a bathroom with an integrated sauna is more of a place to unwind, so instead of stimulation, relaxation – which is rarely achieved with white plus spaciousness, rather like has it. Also many accessories, pictures and restless plants, where small leaves tend to dance, do not offer coziness. Many things need a "frame", which is usually the solid-colored background, not a tile corner here and there, picture frame/corner etc. to the wallpaper, that usually looks restless instead of grounding. White/light walls open up (therefore white on the walls is recommended for small rooms, the darker and/or of the same tone, the more relaxing and harmonious. While many here rather seek a grounding connection to the bathroom, you are different there. You focus differently, and that is why the bathroom will be "okay" for you as well. Very likely even more ;) You will love it. However, it makes sense to engage with colors and the effect of space, textures and surfaces – because often you live in a room and constantly have a kind of unease at your neck – and then it is very likely that the design, without knowing it, is the reason. (Less likely is the man with the knife behind the shower curtain ;) )