For a more relaxed atmosphere, you can find colors from whites, ivories and creams to pastel shades of green, blue and pink. Also look into choosing a fabric that matches other fabric colors in the room. As opposed to the more sedate, "sleepy" soft tones, don’t be afraid to venture onto the "dark side" and choose a darker and heavier fabric for your headboard. Darker fabrics work very well in a larger master bedroom that already is quite dramatic or romantic. Deep blues, magentas and greens can be very effective for getting this effect.
The trick with a double bed is to simplify the entire look of the room (no clutter) and go with a more "reserved" look for the room. Keep the room as clean as possible; otherwise it may look as if the bed is lost at sea with your belongings! Another trick to give your double bed more of a profound appearance in the room is to invest in a good quality headboard. You may also want to consider finding a headboard with rounded edges to further compliment the simplified look.