I would start by adding some natural colors -- you don't want to be too severe when adding color. So add some greenery first -- if you don't have a green thumb, Pottery Barn and Ikea carry fantastic artificial greenery. Jade plants and other succulents always look great too and are hard to kill. Then add a few pillows or a rug that has some color in it. Also focus on textures and finishes -- glass, chrome, brass can all bring a taupe color to life without adding so much "color".