Yes, this can be true. A deep color, particularly if you paint the ceiling as well, makes the walls seem to melt away from you. It will also make the corners where the walls meet and the ceiling meets the walls sort of melt away, because you don't see the shadow lines as clearly. This works best with a soft neutral color, or a neutral version of a color...one that is greyed down. What doesn't work is a strong or hot dark color,like bright dark blue, or orange, or bright yellow, which can jump right into your face in a small space. Think foggy, atmospheric colors with warm undertones, because whatever strong color you choose can reflect onto your skin...so be sure you have enough lighting for your face at the mirror, so that you don't look dead when you look into it!

Photos will help. It all depend on how much trim you have and if it is natural or painted. Vanity or sink? What color fixtures? What lighting do you already have? Wall tile? How much?

I used a dark color, would I paint the ceiling the SAME color or a lighter shade of that color? Unfortunately, I don't have a picture of the bathroom. The floor is a light brick colored tile. The vanity and mirror are Antiqued White Vintage with dark oil-rubbed bronze hardware and over-the-mirror light (from Lowe's - link following)
http://www.lowes.com/pd_168072-444-C15524_4294855867_4294933768?productId=1217333&pl=1&currentURL=/pl_Bath%2BVanities%2Bwith%2BTops_4294855867_4294933768_

My master bath shower/toilet room is called Park Bench (think of the green of park benches from the past). I love it. The ceiling is still white (that will change to an almond one day). It has no natural light but a bright light. It is very calming and I don't feel closed in at all. I'm not a morning person and frankly, it helps to transition me into the day. I could not take a bright room at 6am.

I have a small bath (no natural light) and I painted it with a base color of pale gray, I then sponged on silver metallic paint (Sherwin Williams) and it looks great.
The silver metallic catches the light and really opens up the room. It was easy to do as well. Just play around with the sponging pattern on a practice board, I used a small natural sea sponge and applied it in a tight pattern.