The colouring (English spelling) of natural diamonds is entirely natural, and affects the value. Blue-whites and whites are worth the most and yellow-browns (the most common) the least. Pinks are somewhere in between. Very occasionally a diamond appears that has several colours in it. These are often cut to make best use of the variations.
Blue
Boron impurities are responsible for the color of blue diamonds. From light to sky blue to nearly navy, the cool blue color in diamonds exhibits a wide range of intensitie. Yellow
The most famed of natural colored diamonds are the yellows, often marketed with less pejorative nomenclature as "canary" diamonds. The presence of nitrogen impurities make for the yellow color. Green
Green diamonds result from radiation. After diamonds form deep within the earth, radioactive rocks emitting radiation nearby color already formed diamonds to green. Such natural irradiation occurs over millions more years. And the green color occurs towards the surface rather than throughout the stone. As such, natural green diamonds show low color saturation and have a grayish cast. They are, as well, exceedingly rare.
Impurities in the diamond when forming cause coloration. It only takes about 1 atom per million diamond lattice atoms. Boron = blue, nitrogen = yellow, lattice defects = brown, radiation exposure = green. They also come in purple, pink, orange and red.
