Color paint?

Sherwin Williams Sea Salt is a great color for small bathrooms and it's rather versatile. Accent with white trim, flooring, and fixtures.

Hello light colors generally make a room feel brighter and more spacious particular rooms without windows. What color is the flooring that might impact your color choice.

Often it’s less about what color and more about how many contrasting colors are in the room. Keep the scheme monochromatic and It will appear bigger. Most people say light colors are best.

Keeping walls light in color and the less "break up" of the color such as on window and door trim the larger the room willl appear.

With or without windows? Most lighter colors are popular choices. However if this is a guest bath and not needed for makeup application, you might consider having some fun with it by using darker shades to set a mood and make a statement. My friend did this and have seen many a magazine spread with gorgeous examples. You might try an accent wall and add molding for effect. Or go simple on the color scheme and bring in pops of color with accessories and linens. One can take a plain light colored bathroom and make it fabulous with shower curtain, rugs, towels and various countertop accessories, but keep it to a minimum so not to appear as cluttered which is visually distracting. Just have fun with it!

I find darker shades make a small room feel larger. The walls recede visually that way. If the room is dark, light colors will look dingy.

If you place LED lights on the bath exhaust fan, on either side of the vanity mirror (mounted aout 60" off the floor), and over the tub, the bath will definitely appear larger. Place the lighting on dimmers, and look for 3300-3500 Kelvin fixtures. Using a gloss or semi gloss bathroom paint increases reflectivity and deals better with humidity. If you have tile in your bath, it will further reflect light. Some people install Solatubes or skylights, as well. Take numerous color chips home and tape them to all 4 walls. Check these out at various times of day/night.

Using chrome fixtures will also increase reflectivity.

White