I see mostly blue accents, especially from the major features like the rug. That's what I'd go with! :-)

Thanks! Any blues you recommend?

There is no way to tell what color would work through a computer monitor as they all show differently. I'd go get some sample cards to see what colors go with the room. :-)

Light sky blue, pulled from rug.

Color Zen how about Benjamin Moore Hale Navy?

I would not go that dark, too stark for your room.

You can start your search on Pinterest and then grab some sample pots

With your situation, I would definitely suggest inserting removable painting panels in the bookcase. If you ever wanted to go back to the white, you could just pull the panels out.

You have a lovely room! The colours you’ve chosen and your furniture all work well together. The backs of your bookshelves would look great in muted blue or green. But!! I think the first thing you should do before painting, is style your shelving better. You’ve got a lot of small knick knacks which tend to look really cluttered. Have a look in Houzz and see how the pro’s do it. There’s a LOT of pics. Think about adding larger scale pieces like decorative boxes, vases, bowls, baskets, all in the colours of your room. Adding a lot of books will help. Like I said, your room is lovely and you are certainly on the right track with the style you’re going for. The focal point of your room is definitely the wall of cabinetry. Make it become a dazzling feature! I think once you have it styled beautifully, you may not want to paint it.

I think a muted light blue or greenish blue could work. If you're not sure of the color, paint a sample on poster board cut to fit the back of the shelves. You might also consider using the color on the walls instead, and leaving the shelves white.

My Houzz: Traditional Home With Cottage Flair · More Info

Thanks to all the great ideas! I was thinking of may be wallpaper and like this one! Any thoughts:

https://www.flavorpaper.com/wallpaper/murals/fracture

Wallpaper is a good idea, but I'd order a sample to fit one shelf before you decide on that one. You may lose most of the design from a distance and behind other items, and it may be too dark and harsh.

Your shelves look to be at least 8" deep, most standard books are somewhere 7-8" deep. I know you didn't ask that, but if it were my space, I'd quite honestly fill the heck out of this bookcase with books. I seem to never have enough space for my books, regardless of the house size I live in. I swear they multiply at night, when I'm not looking :).

Below is a design we did for a client. Perhaps looking at this image will aid you with your dilemma.

High-End Residence · More Info

Very pretty. The grey looks very nice in the setting! Any color you can recommend ?