The colour of every piece of diamond varies slightly.  As seen from the chart, the different natural hues are classified into 23 grades starting from D to Z.  

The most rare and valuable is the colourless gade D, while colours of grades M to Z are recognizable with the light yellow grade Z being the lowest of all.

The colour of a diamond plays a crucial role in determingin its worth.  While "colourless" diamonds are extremely rare and valuable, the most common are "near colourless" and "light yellow".  The rarity and worth of a dimaond directly relate to its intensity of whiteness.  Similarly rare are "coloured diamonds" that are even more precious than their colourless relatives.