Your room doesn't need to just be a utilitarian workspace that holds all of your stuff. You'll want to decorate it in a way that keeps you and your work fresh and inspired. White walls are for museums, so pick a paint color you love that also accents the room's features. Blues and greens are cool colors, which could be a good choice if you want to inspire some calm during your sewing hours. They also make the walls appear to recede, which is helpful in small rooms. Reds, oranges and yellows are warm colors that can make a larger room feel cozy and comfy.
You can always decorate with art that you like, but sewing supplies often lend enough color and texture to a room that you may not even have to bring in extra decorations. If you have a colorful collection of fabrics that you love, don't tuck them away behind closed doors; store them on open shelves so they become part of the décor.
Decorate the room with your sewing creations by sewing slipcovers for chairs, valances or drapes for the windows and cushions for benches. Dress forms and mannequins are good sewing décor, even if you don't sew clothes.
Carpet may be preferred from a comfort factor, but remember that you're going to have tons of little scraps of fabric and snips of thread to clean up on a regular basis, so it may be easier to use a broom and dustpan on bare wood floors than to drag out the vacuum.