It's neither it is a sofit that is used to cover pipes,steps ,roof angles ,stuff like that.
Now if you trying to paint it you could go with the one and paint it the color of the ceiling or if you feel it is part of the wall you could paint it to match the wall but why would you wanna do that for use it as an art peice pait a completely different color to contrast with the other two colors and if you know of an "artist" or someone who can draw really well have them come over and do a murel (sp?) on it like steel gerders that will make people think about what is holding the ceiling up lol. You could always paint an outside sky theme on it as well that will give you the feeling that you have nothing hanging there. it the end it is up to you of course but I vote neither.