Our standard conception of diamond is as a colorless stone. But color in diamond exists in myriad variations, from dazzling pinks and yellows to blues and violet. A chemically-pure, perfect crystal of diamond is colorless, but add a little nitrogen and yellow appears. Add boron instead and a blue diamond results. Colors from red to violet, real white, and black are possible and can be complex to understand scientifically.
Colored diamonds are hot, both in the marketplace and in science.
To understand color in diamond, one must remember that light is a form of energy. In this representation of the visible spectrum, low energy is at the bottom and high energy at the top. Each color of the rainbow corresponds to a particular energy. When the energy of light entering a diamond equals the amount needed to bump an electron to another configuration, parts of the spectrum are absorbed. A pure diamond is colorless because visible light lacks sufficient energy to excite any of its electrons and therefore no light is absorbed.