The ideal diamond is completely colorless. These are the most expensive types of diamond. Though most diamonds appear colorless, they actually have slight tones of yellow or brown. The Gemological Institute of America (GIA), the authority in diamond certification, grades color alphabetically from D (totally colorless) to Z (heavily tinted).
The difference in grades is very subtle, and mostly not visible to the naked eye. A diamond with a visible tint such as K and above can still be beautiful if it has a good clarity and cut. Only diamonds graded N onwards have a tint that is visible to the naked eye. Beyond S the tint grows more intense. Natural colored diamonds come in all shades and colors of the rainbow. The most popular colors and diamond types are a combination of pink, blue, brown, yellow, orange, green and red. Yellow is the most common naturally occurring color in a diamond.