white no comment on the paint selection

For trim (with almost any color), I have always used Pratt & Lambert's Silver Lining. If you go to a P&L dealer, they can make up a quart-sized sample (eggshell only) for like $7...it is a great trim color. HTH

I think that will be pretty. Your trim work looks very similar to mine - dark stained pine, so don't hesitate to paint it - I painted mine many years ago. You have a warm toned home. So consider staying with warm tones. If you want color, SW Sea Salt has green, blue and gray tones, but works well with warm woods: From Hooked on Houses: Computer do not show true colors well, but I have a cream with a hint of beige. This is the upstairs hall with a beadboard wainscot: https://www.houzz.com/photos/my-pics-work-in-progress-phvw-vp~88642832 That color is a little warmer than the Sea Salt. It is also the color I have in my kitchen - pics in my "my pics" idea book.

IMHO, this does not look good at all. I would not except this solution. It looks like you just slapped up a piece of molding. It needs to be integrated more with the existing chair rail and base molding. If you move it over to start under the chair rail, it would be too close to the boxed out trim. If you want it to look like it is meant to be this way, he really needs to move the trim under the chair rail and shorten the width of the box so the spacing is the same as the distance between other boxes. Also, the trim piece should not stand proud of the base piece. You need someone that knows how to rework this to look professional.