I think you leave it white like the ceiling, if anything it kind of breaks the room up nicely.

When I encounter this scenario, I always paint the entire structure the same color as the walls so that it will blend in and not attract anymore attention to itself.

I don't think there is a correct way as such, it's up to your own taste and also the style of your furniture.
Personally i'd paint to match the wall, the form alone gives enough interest for me.
You could try both and see which you feel happiest with, after all it's only a small surface to paint then repaint if necessary.

Pretty color and all very relaxing for a bedroom, i'm sure whatever you do it'll look great.

If you are trying to call attention to the architectural aspect then use the contrast. However, I would paint it the wall color...It is not the ceiling. I agree with Magada, there is enough interest with the structure itself...no need to draw additional attention to it.

In this case paint it the wall color...it will draw attention away from this area.