The colours you use in a bedroom can make a huge difference in whether it feels airy and open or dark and cloistering. Using cool colours, such as white and pale blue can make any room seem larger. Just as using neutral tones does. In order to make a room seem bigger, you need to first address the colour of the walls.
If you live in a rental, the good news is that they're probably already painted in a room expanding colour, white. If you have your own home and have darker, warmer colours on for the walls and ceiling, it may be time to change to create a more open feeling.
Warm colours and room size
Warm colours are cosy and yet they can make a room feel smaller, particularly brighter warm colours. They include colours with a base of yellow, orange and red. Blue, white, grey and green are cool colours. These tend to expand a room and make it feel larger. You can create an illusion of space by using cooler colours on the walls and floor to expand your space. That, however, does not mean you'll have to decorate with strictly green or blue or keep only neutral tones in the room.
Decorate it with accent pieces, including your bedding, and stick with lighter shades such as neutral tones, particularly for the bedspread or duvet cover. You can have a pattern, but keep it small and muted. Drawing attention to your bed with bright colours dwarfs the rest of the room.
Blending the bedding with the wall is one way to add to the illusion of space. If you want some brighter colours, consider using accent cushion and small decorative items to bring in the colour. Duvet covers with a muted soft small pattern work far better to add a more spacious feeling than those with a larger brighter pattern.
Stripes and size perception
Stripes make a room seem larger. Use vertical or horizontal strips to make the room seem longer or wider. If you want it to look wider, the stripes should go across the width of the room. For a longer appearance a duvet cover with the stripes going up and down. You can get the same effect and use them more sparingly by adding a striped bed runner at the end of the bed to accent a plain duvet cover.
You don't have to use only blues, greens and grey to make the room spacious, a mix of light pastels adds softness and still maintain a roomier feel. Stick with paler pastel shades for bedspreads and duvet covers and use a monochromatic scheme for accents, pillow cases and sheets.
For instance, a pale lavender duvet cover would look stunning with a rich deeper purple tone for pillow cases. Purple is the compromise that blends the warmth of red and the cool tones of blue, just as green is the blend between yellow and blue.