Colored diamonds are found both in nature and in laboratory settings.  According to the GIA, only one in 10,000 natural diamonds is a colored diamond outside the D-to-Z grading spectrum.  Colored diamonds can be found in almost any shade of the rainbow.  The GIA lists 27 different hues for natural colored diamonds.

Even a one-carat diamond requires billions of carbon atoms to bond, and all of those atoms must be carbon to create a colorless diamond. The slightest quirk creates a colored diamond: a bit of boron makes a blue diamond; nitrogen makes a yellow diamond; natural radiation form nearby rocks trap electrons to create a green surface color; pink or red shades are thought to be due to changes to the electron structure during the voyage to the surface.

The GIA can issue color grades.  It describes the color of fancy diamonds in three ways: pure spectral colors of the diamond (hue); lightness and darkness of the hue (tone); and the color’s strength and purity on a scale from neutral to vivid (saturation).  Natural radiation and pressure can intensify the diamond’s color.