Natural yellow diamonds or as they are knows commercially as Canary diamonds are really impure diamonds. Diamonds that have Nitrogen atoms placed in the natural Carbon structure of the diamond become yellow. The more, so called, impure the atomic structure is the more yellow the diamond becomes. A pure Carbon structure in a diamond would yield an absolute white diamond but finding those are very hard as well. The GIA defines 4 yellow shades in the Fancy range for yellow diamonds. Light, Fancy, Intense and Vivid.