Yes. Needs to match

I think the beadboard can be a nice contrasting color. I've seen people paint the wall/beadboard behind cabinets all kinds of colors!!

Yes have seen some nice blue painted beadboard.

Oh yes, paint it a bright contrasting color!

Match the color of the breadboard to the most dominant pastel color in the room. For example, the blue on the map. Or have it match the color of the cabinet.

What will go in the cabinet? I have a cabinet at our lake house that stores a milk glass collection. I painted the back of the shelves navy to make the dishes stand out. Just a thought.

I would paint it so that it doesnt look like an addition to the space. Painting it will help it blend into the space instead of obviously being the new addition to the room due to the contrast in color.
-M.M.

Actually I am leaving it white. It is in a bedroom I decorated for my grandson and will be used by guests as well. There is lots of color in the room already. Went with red white and blue and love how it turned out. The cupboard may store some toys. Bought baskets to fit.