It's a little odd to shiplap the two walls that are across from each other in a powder room. Why not shiplap the entire room and use a more interesting floor tile to bring in some color and/or pattern? Otherwise I'd just shiplap the vanity wall since that's your focal wall. A toilet shouldn't get the same treatment as the vanity wall.

i like the kentucky haze best, or would even go a little lighter and fresher, like a light robin's egg blue? i think light blue goes really well with white and greys.

Look at BM Horizon. Its a very pale blue with a touch of green. I like your Kentucky Haze that is shown on your strip of colors. Could you find a lighter version?

Yes, shiplap on one wall should work. it looks like that is what is done on all of your inspiration pictures. I also like Benjamin Moore Yarmouth Blue. Here is a link to it that includes shades that are lighter and darker than it is. A lighter shade could be good, too. Yarmouth Blue

I'm confused by your description of your walls. You said toilet and sink "walls", which means they are on different walls, so I assumed they are across from each other with that room size. That means the two 3' walls would be shiplapped with a painted 6' wall. That's what I'm advising against.

I have seen photos on Houzz of the entire bath shiplapped partway up like a tall wainscoting with paint above. Search on shiplap/powder room for examples.

Love the vanity. Would you mind providing details for it. I have very small bathrooms and that furniture look would be perfect. Thank you.

Every one of your photos shows shiplap on just the vanity wall. It's treated as an accent wall. Sometimes you see the vanity wall in a powder room covered in tile--same thing.

Powder Room in former closet by Bay Area Contractor · More Info

Here's a search on shiplap in powder rooms.

https://www.houzz.com/photos/powder-room/query/shiplap/nqrw/p/32

rickie95 thank you. It is really nice but too wide I can't do more than 24" but now I have an idea of what I want if I go custom.