Don't go with a dark gray carpet UNLESS you love vacuuming as every piece of lint or dust is going to show up unlike a lighter color that hides a lot of stuff.

Another thing to keep in mind is that the darker the floor and walls, the darker the room is going to be. That may seem romantic now, but down the road, you're going to end up with a bedroom that is like a cave.

If you want a calming color, go with green. You could go with a light grayish green that would be calming without turning the room into a cave. Gray blues are also very nice as are olive greens. You could even go with a lighter brown. Here are a few colors that would look nice:

This is the color my living room, dining room, kitchen and hallway is. I can't tell you how much I love it. It's very soothing:

http://www.behr.com/consumer/ColorDetailView/PPU10-17
http://www.behr.com/consumer/ColorDetailView/750E-3
http://www.behr.com/consumer/ColorDetailView/HDC-NT-09

The great thing about behr's website is that you can apply different colors to pictures in the 'preview a room' section. It helps you get an idea of how different colors look. It will also help you get a feel for color.