There are a range of diamond colour gradings, this starts from D being the highest all the way down to Z being the lowest.
D colour: Highest, absolutely “colourless” grade, appreciated best set in platinum or white gold. Exceptionally rare.
E colour: A “colourless” grade appreciated best set in platinum or white gold. Traces of colour difficult for even trained eye to detect.
F colour: A “colourless” grade appreciated best set in platinum or white gold. Faint colour detectable by a trained gemologist.
G colour: The highest “near-colourless” grade. Colour may be detectable when compared to much higher “colourless” grades. Excellent value.
H colour: A “near-colourless” grade, colour is only noticeable when compared to much higher colour grades. Excellent value.
I colour: The last of the “near-colourless” grades, colour may be only slightly detectable upon close examination. Exceptional value.
J colour: Colour may be slightly detectable to the unaided eye, particularly in fancy shapes or diamonds over 1-carat.
K-Z colour: Colour is visibly subtle to distracting. if you buy from Blue Nile.com they do not carry diamonds of these colour grades.