The highest colour grade given to a polished diamond. D colour diamonds are the highest graded on the 'colourless' section of the scale, and lack any sort of hue.
The second grade of the 'colourless' section of the colour scale. E colour diamonds have some hue which is extremely difficult to detect even by a trained gemmologist.
The final grade of the colourless section, f colour diamonds represent diamonds with a slight hue that is difficult to detect by the untrained eye.
G colour diamonds are the highest grade of the ‘near colourless’ section of the colour scale. Some colour may be detected by a trained gemmologist, however, to the untrained eye, it is difficult to detect any sort of colour or hue.
H colour diamonds are still part of the ‘near colourless’ category, colour is only visible in bright light conditions or when seen with a sophisticated eye glass.
I colour diamonds only show colour under bright lighting conditions or when examined closely.
J colour: The last of the "near-colourless" grades, colour may be slightly detectable to the unaided eye, particularly in fancy shapes or diamonds over 1-carat.
K colour: The first of the "faint" colour grades, meaning colour may be detectable to the naked eye. K-colour diamonds can offer great value.