4 Cs of Diamond
D : Absolutely Colourless. The highest colour grade, which is extremely rare.
E : Colourless. Only minute traces of colour can be detected by an expert gemmologist. A rare diamond.
F : Colourless. Slight colour detected by an expert gemmologist, but still considered a "colourless" grade. A high quality diamond.
G - H : Near colourless. Colour noticeable when compared to diamonds of better grades, but theses grades offer excellent value.
I -J - K : Near colourless. Colour slightly detectable. An excellent value
L - M : Noticeable colour.
N - Z : Easily noticeable colour.
The ideal diamond is completely colourless, and the most expensive. However most diamonds which appear colourless actually have slight tones of yellow or brown. SGL, grades colour alphabetically from D (totally colourless) to Z (heavily tinted).
Please note the difference in grades are 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 good clarity and cut. Only diamond graded N onwards have a tint visible to the naked eye. From S onwards, the tint grows more intense. Natural colour diamonds come in all shades and colour of the rainbow. The most popular colour are combination of pink, blue, brown, yellow, orange, green and red. Yellow is the most common naturally occurring fancy colour, white, red, blue, and green diamonds are very rare.