Paint one or more walls apple green, using several coats for a bold, saturated hue and a single or double coat for a lighter shade. For smaller rooms a single accent wall painted green will add color without overpowering a space, while chair rails or wainscoting can add green around the room without overtaking the space.
Use wallpaper, stencils or vinyl wall graphics--or a combination--to add texture to the walls without making the room overly busy. Bold colors can be somewhat overwhelming, so temper bright apple green with simple graphics or patterns rather than intricate designs.
Opt for coordinating furniture in solid black or solid white, which are versatile enough to grow with your teen as their tastes evolve. For funkier furniture, re-purpose vintage store finds with coats of apple green paint or trim, and refinish the piece when you redesign the room.
Add accessories such as throw pillows, canopies, curtains and framed prints to complete the room. A bright green ceiling fan, stained glass light fixture or large suncatchers brighten up the color and add airiness to the space.