Diamond colour is graded against a D-Z colour scale. Developed by the Gemological Institute of America, the spectrum consists of 23 letter grades. Absolutely colourless diamonds are defined by a D grade. Diamonds with an I-J grade begin to emit colours detectable to the naked eye. Most diamonds embody some yellow to brown tinting. A diamond darker then Z is considered a Fancy Coloured Diamond and is priced considerably higher due to its rarity.
The stunning power of a brilliantly coloured diamond is simply irresistible.
The allure of diamond fluorescence is debatable. A soft coloured glow awakened in a diamond under ultraviolet light is a unique effect sought by some and avoided by others.
Strong fluorescence can cause a near-colourless grade diamond to look even whiter. Consequently, excessive fluorescence can create a slightly hazy or oily appearance, decreasing the price of the diamond by up to 50%.