The purest of pure diamonds should technically transmit visible light and appear as a clear colorless crystal. Not every diamond is white; colors in diamond originate from lattice (repeating atomic pattern) defects and impurities. The diamond crystal lattice is exceptionally strong and only atoms of nitrogen, boron and hydrogen can be introduced into diamond during the growth at significant concentrations.
The most common impurity in the growth of diamond is nitrogen. Nitrogen gives the appearance of yellow or brown hues, Boron is responsible for blue hues, plastic deformation can cause pink hues and irradiation can result in green hues in diamonds. Natural colored diamonds that chart past "Z" on the GIA Color Scale are very rare and classified as a "fancy" color. It is said that there is 1 fancy colored diamond for every 10,000 colorless diamonds and for a large fancy colored diamond (1 carat or greater) the relationship to colorless is said to 1 to 1 million.
The Gemological Institute of America (GIA) classifies low saturation yellow and brown diamonds as diamonds in the normal color range, and applies a grading scale from "D" (colorless) to "Z" (light yellow). Fancy color diamonds fall under a different grading scale. The most common range that Windsor uses for diamond sales are "D" through "M" and the diamond chart below demonstrates the slight differences in that range. In most cases, it is more desirable to have a diamond with less color and those diamonds hold a higher value. To learn more, be sure to check out our resource on diamonds.