Um. Well, I'd say plain colorful xD
My walls are yellow, my ceiling is dark sky blue and I have a pink and green line where the ceiling meets the wall xD :P

The walls of my bedroom are boring baby blue, BUT over the years my friends and I have attacked them with various colored markers. Basically, my ceiling and walls are giant sketchbook/signature galleries.

It's good fun. Some interesting things are written up there.. XD;;

my room is really really really plain....sometimes i wished it was colorful.

My wall is that fake wood stuff. So, I guess it's kind of plain. Or it would be if I didn't have posters and cut-outs from calendars taped up everywhere. xD My ceiling is pretty much full of posters too.

My bedroom, is
Purple and Aubergine, wth one wall Blue, and the ceiling yellow.
I freaking love it actually.
but it gets boring quite easily.
but I have so much stuff I cant move it all about to Paint.

My walls are pink, but I've covered them with a ton of posters.

I've got posters like

The 300 (x2 different posters)
TMNT (x3 different posters... I love the turtles)
National Treasure
Fight Club
The Crow
Nickleback
All america Rejects
Walk the Line
Nightmare Before Christmas
An optical Allusion poster... it's really cool looking. =]
Blades of Glory
Saiyuki
Batman
Justice Leuge
Elvis
CSI: Crime Scene Investigation
My Chemical Romance
Edward ScissorHands
Sweeny Todd

... I like posters.

Colorful. It makes me happy. I have pictures of roses(my favorite flower) and my stuffed animals on the wall.

Mine is sort of plain. :/
Hm.
I guess I just never had the time to change anything in it.

sadly mines is plain. D:
i have to share a room with my older sister, and well. we're complete opposites. she likes plain soft colors while i like bold colorfulness everywhere. :P

My wall itself is avocado green so I guess that makes it colorful in and of itself. XD But I also have wallscrolls and pictures stuck up on it so yeah, it's pretty interesting. Before the walls were painted I had an ever growing collage by my bed... Unfortunately it had to come down. T^T

Plain, pale pink wall colour.

Mine is plain.
I seriously need to do something with my wall.
I've always wanted to paint it or have someone to paint a mural(sp?), but my mom doesn't allow it. D:
I'm too lazy to make a collage and pin them up.

The walls in my room are plain very pale violet/blue colour. However I've stuck some pictures up, most of them are ones I've done myself, and two are posters.

So my room's walls look like a child's room because of the drawings.