Most diamonds fall in a normal colour range from colourless to slightly yellow, brown, or gray. Actually, diamonds come in all colours, those with distinct, attractive natural tints are called fancy colours.
In the normal colour range, slight colour difference in diamonds of comparable Weight, Clarity, and Cut can make a substantial difference in price. A diamond, 100 percent pure carbon, in a perfect uniform crystal arrangement, would be absolutely colourless. Most diamond crystals pick up some other atoms during their growth process. When nitrogen atoms replace some of the carbon atoms in a diamond crystal, it begins to show a slight yellow tinge.
Diamonds drop in value, as their colour becomes more noticeable, until it is dark enough to be considered fancy.