A bit of a can of worms here. I would leave all trim white and either remove the picture frame molding below chair rail or paint it the same color as the wall behind it. I don’t prefer the look of that picture frame molding contrasting the wall behind it.

Agree with the above. I think it would be a mistake to paint your crown molding or the casing in the opening to the living room the wall color. While you may see this being done in pictures online, this is a trend, and it's something you would be more likely to see along with modern decor. It looks like your decor is more transitional, so no need to lean too far modern. Painting trim is a pain. Since you or the next person who lives in your house might want it white again, just skip that step. Just make the part under the chair rail all one color. I would have told you to remove the chair rail since you're considering painting it out, but you have that shelf like effect going on in the opening, so clearly you can't remove it. Before you paint it out, think about how you're going to transition the color into the living room. Because I can't see the other side I'm not sure how that would work.

Thank you all so far! Great insights! I think my main issue is how to paint the chair rail the same color as the lower walls (as it seems as though the white chair rail is definitely screaming early 2000s) but it’s difficult as it leads into the arch. Do we paint the shelf that leads to the arch but keep the arch white? Will that not flow well? TY

Painting the trim and wall color the same color is generally a full-monochrome look, not another combination of dark and light.

Here there is actually paper above the wainscot, but the idea is that there is one paint color throughout

I would leave it white.

I would leave it all white.

Leave the arch white. It is woodwork.

Leave the chair rail white. It is wood work.

Repaint the wainscoting white.

Agree with last post. Trim color below and wall color above.

Or everything one color as shown by Palimpsest.

Thanks for your feedback but can’t paint the lower panels white. The wall flows into the living room which means I would then have to paint the living room white. We’re turning it into a library so prefer it to be a moody dark color

Could you identify what you were planning on painting what and the relationships of the rooms?

Sure, walls in both rooms will be painted. The Room with the leather chairs (formal living) will now be a library with bookshelves and a record player. Painting it a deep moody color (BM Narragansett Green). The room flows into our formal dining room, the color will flow to the lower walls. Would like to paint all lowers the wainscoting and chair rail, also Narragansett Green. Uppers dinning wall color is TBD. Don’t think I can continue that dark of a color up too. Would love to wallpaper but not in the cards right now. Main issue is how to paint chair rail to flow to arch?? Paint chair rail and shelf of arch but keeping the arch itself white or also painting? I have considered painting the crown molding but worry if the trend will not last long. Thank you. Appreciate any feedback.

Are you open to altering some of your trim? For instance, continuing the arch down to the floor, either through the chair rail or removing the chair rail from the arch? That could give you a natural break to change paint colors from library to dining room.

But I'd keep all trim white. Will you have bookcases behind these 2 chairs -- will they contribute to a 'break' between the two rooms?

It looks like the two rooms have complete ceilings meaning there are actual doorways or arched openings between spaces and the crown molding does not bleed into any hallways or other spaces like that.

I think the problem is that the archway is not complete, it's truncated into that base or plinth that wraps between the two rooms.

The safest and most classic way to deal with this because of the arch would be to keep the trim white and paint all under the chair rail white in the dining room because it has that paneled effect. But this is kind of going to kill the look you are going for. And you can't really keep just the arch trim white because it will float above the deeper colors and not be attached to anything.

For me I think the issue would be the dark trim on the dining room side on top of the lighter upper wall color you have planned.

Yes, so what should I do? Isn’t having a white chair rail very outdated? Do I have the the arch painted dark but keep the crown-molding, doorframes and baseboard white??

No removing of woodwork. This is a paint job only. Bookcases are not splitting the rooms they’re going against this wall (pic attached)

White wainscotting, is never dated. It has been around for many years, and will be around for many more, and even if it was, I wouldnt worry about trends for anything. Trends come and trends go. There is no point in even trying to keep up with trends.

Here’s the coordinating colours Benjamin Moore suggests for narragansett green.

Curious what colours are in your china/dishes.

I would call white chair rail/wainscotting traditional not dated. i’ve lived in many older homes with it (ie 1920s-40s). i certainly don’t associate it with 2000s. :) i wonder about painting the bottom inside of arch white then dark color on the livingroom side. agree its tricky!

Completely agree that white wainscoting is classic. It just won’t work with this setup due to the formal room spilling into the dining room with bottom wainscoting. Not looking to paint the formal room white. I do believe that a white chair rail with 2 colors is becoming outdated. Trends do come and go, but based on what you see on Pinterest and magazines a white chair rail may make the room look dated.

Appreciate everyone’s feedback. It’s helping me look at it from every angle. An idea that has come up is the arch trim on library room side to match the dark walls and on the dining room side arch trim to match the upper walls as well as the underside on the arch to match the lighter dining room upper walls. I guess it’s something that might work.

I do think the white chair rail only with two different wall colors above and below is dated, and I don't much like that word.

It is possible to change colors at the archway, particularly if they are closely correlated, although that's not a popular look, particularly on GW.

In that case you stop the dining room color at the arched opening on the DW side and the embrasure of the arch headed could all be the Narragansett Green as well as the entire living room. The problem here is the extra thickness of that wall at the bottom.

Are you refurnishing the living room after the dark paint color? That leather furniture is going to look kinda light and cognac-orange with that dark blue-green I think. I am not sure that's what you intend.

Would you take one more photo of the arch, but take it from the living room? Want to see how the chair rail ends.

To give an idea of how it all works.
Now my latest thought was Painting top and bottom of Dining all a lighter gray or greige including the chair rail and arch on all sides. The tricky part would be where the cut off may be on the small end of the arch wall. Still have it light and then just have the entire formal room the dark color just don’t know if that transition would look odd

I think at the very least the dining room has to be some version of the Narragansett Green, or some light blue green that works with the Narragansett Green for these two rooms to pair well together. I don't think a greige is going to do it.

"The tricky part would be where the cut off may be on the small end of the arch wall."

That is what we all are dealing with...the arch should have come down to the floor, giving a true separation from one room into the other. With the chair rail wrapped into the living room and abruptly cut off is just wrong. An arch isn't a column, and visually, should be grounded.

This is the only thing I could come up with:

Have bookcases built on living room side. That will "explain" the chair rail.

So, new bookcases, painted your trim color and the tiny wall UNDER the arch gets painted trim color (same finish). Visually, you will see white to the baseboard.

One more question: which room do walk into first from the front door?

No construction work on this project. Just paint and updating the light fixture. 2 large bookcases are being delivered tomorrow. Rooms are going to be painted in a little over a week. Formal room is what you see to the far right through the front door but you mainly see dinning room due to more common areas of home. It’s off the kitchen and can also be seen from the family room.

View from foyer and kitchen

I love this arch treatment, it might be a bit whimsical for your space. If you did it I would make the variation in the stripe colors very subtle.

https://bobbyberk.com/how-one-designer-created-a-beautiful-breakfast-nook-in-just-3-days/

No sure if I should go for something more like this and keep all arch trim dark. But would baseboard and crown molding not fit the vibe as it staying white?

I agree with @elcieg -- for me, it would not be worth creating a disjointed paint/trim color combination to have dark paint do all the design heavy lifting for these rooms -

if I wanted a more moody space, I would paint everything below the chair rail the trim color for cohesiveness, add a dark and moody color above, then create drama with much more substantial/lush curtains, a more dramatic chandelier (sounds like one is on order), darker rug, large scale art that is fabulous etc (removing the small display cab and undersized wall art in the DR will help)