D: Colourless

A "D" colour grade for a diamond is the highest and most desirable grade on the Gemological Institute of America (GIA) colour scale. Diamonds with a D colour grade are considered "colourless”. D diamonds are exceptionally rare and valuable because they appear completely transparent and devoid of any visible hue. They are often described as "ice-white" or "pure white."

E colour diamonds are just one step below the highest grade, which is "D" for colourless diamonds. They are almost as colourless as D diamonds, with only a faint trace of colour that is typically not noticeable to the naked eye. E colour diamonds are known for their exceptional brilliance and sparkle. They allow a significant amount of light to pass through, which creates a stunning play of colours and a high level of fire.

F colour diamonds are in the near-colourless range, just below the highest grades (D and E) for completely colourless diamonds. They are exceptionally close to being colourless, with a very faint hint of colour that is typically difficult to detect with the naked eye.

G colour diamonds are considered "near-colourless," indicating that they have a slight hint of colour, but it is generally challenging to spot with the naked eye. The presence of colour in G diamonds is subtle and usually only noticeable when compared to higher colour grades. They allow a good amount of light to pass through, resulting in a play of colours, strong fire, and scintillation that contribute to their beauty.

Colour H for a diamond represents a "Near Colourless" grade. While it has a faint hint of colour when compared to the top grades (D, E, and F), it's generally not visibly noticeable to the naked eye. 

Colour I for a diamond fall within the "Near Colourless" range. It has a slight hint of colour, but this is typically difficult to detect without close examination. 

Colour J for a diamond is considered a "Near Colourless" grade. It has a slight but still subtle hint of colour, which is generally only noticeable when closely examined. 

Colour K for a diamond fall into the "Faint Yellow" range. It exhibits a noticeable hint of yellow or colour, which can be visible to the naked eye.

A diamond with a colour grade of L is categorized as having a "Faint Yellow" colour. The presence of this faint yellow tint is typically noticeable, even to the naked eye.

These diamonds would be considered in the "Faint Yellow" or "Very Light Yellow" category indicating the presence of yellowish hue, which becomes more pronounced as you move down the colour scale.

The "N" grade indicates a diamond with a noticeable yellow or brownish tint.