Perhaps the strongest way to incorporate this color scheme into the room is with wall decor. A simple coat of paint in any one color or a combination of purple, blue and black will form the basis for the room's palette. Instead of paint, consider using a wallpaper print that features these colors. This is a hassle to remove later, but it can make a big statement even in a small room. Instead of wallpaper, paint a mural or use stencils to paint these colors on the wall.
The focal point of any bedroom should be the bed itself. Use these three colors to frame this area. For example, choose a plum duvet cover for the bed. Accent with aqua blue pillow shams and a black bed skirt. Throw pillows and blankets in bold prints, such as polka dots, stripes or chevron patterns, will work so long as they are in keeping with the purple, blue and black color palette in this space.
A teenager's room is an opportunity to get a little wild with decor, so paint ordinary pieces of furniture to help them better match this space. For example, paint a nightstand blue with black and purple accents along the trim work. The art and accessories will be what completes the look of this space. Don't forget to incorporate these colors into overhead lighting, lamps, floor rugs and curtains. For a graphic wall display, let the teenage girl paint canvases in her favorite colors for a modern art-inspired look.
Select the shades of purple, blue and black that coordinate with your chosen decorating scheme. For example, if the style is traditional, choose a plum purple with a royal blue. If the style is soft and contemporary, you may prefer lavender and baby blue. If the scheme is bold and "out there," incorporate splashes of teal and neon blue. This combination can be as dramatic or as subtle as your chosen design style dictates.