You are lucky in that both your bathrooms are super neutral and you don't have any major uglies going on. Painting the walls a white I think would look great as long as the underlying colour in the white went with your tile. I would change the mirror above the small vanity. Looks like the existing mirror may be a medicine cabinet so I would get rid of it and go with a decorative mirror with some personality. The window in your bigger bathroom looks weird. The blind looks way too big for the window and the sill below the window also looks too big. Did the previous owners make the sill to match the size of the blind? I would replace the blinds in both bathrooms and put up some kind of blind or curtain that uses print fabric with colour just to get some interest going. I would also consider painting the vanity in the larger bathroom a colour and change the door hardware. Use one kind of knob and put in the corners of the doors (looks weird having a handle in the middle of the door) and a knob in the centre of all your drawers including the unusable centre panel (looks weird not having a knob there). Add decorative rugs to both bathrooms to get some colour in there and replace your towels with coloured ones. So, add colour to both rooms with towels, rug, blind/curtain. And by colour I mean grey or brown or an actual colour. Something with contrast and not just white or cream.

First do not do the herringbone in the niche in fact don’t do the niche at all IMO they get skuzzy , there is no reason to want to highlight a bunch of shampoo bottles and if you are going to have a leak this is one of the weak spots in a shower. If you must do it then that herringbone needs to be somehwere else in the bathroom. As for wall color I like watery colors in bathrooms. Like these types of color. I really like the Harbour Haze .

Hi! The shower backsplash looks amazing! Benjamin Moore's White Dove and Chantilly Lace are great cool toned white paint as well as Sherwin Williams' Pure White. Best of luck!

I would choose a very light version of the lovely blue/green color that is in your wall tile. Very pale, just to add a hint of color to your walls. If the color leans to the green side, you might look at BM Sea Salt. If towards the blue, BM Silver Cloud.