It is often perceived that diamonds set into jewellery are colourless, but most are near colourless or slightly yellow. The average colours used would be G to I colours.
When graded, colours of diamonds are determined by comparing them to a master set. Each letter between D & Z represents a noticeable shade of colour.
Some diamonds can emit a visible tint of blue light when exposed to UV rays i.e. from sunlight. But this is not a factor in determining colour or clarity grades
Due to the way natural diamonds are formed under extreme heat an d pressure, it is very rare to find a diamond that has no internal or external flaws.
These characteristics allow gemologists to differentiate individual natural diamonds from synthetic and simulate diamonds.
Clarity refers to the presence (or absence) of impurities, blemishes or other identifying characteristics within a diamond. Clarity characteristics are what make every diamond completely unique. There are no two diamonds that will have exactly the same inclusions in the same location.
The grades are determined by the way light behaves within the diamond and how it returns to your eye. Characteristics like fire and scintillation (flashes of light and colour) are taken into account when grading the cut.
It is the proportions and symmetry of the diamond that affect the way light behaves within it, and as a result, affects its overall appeal. Thus why cut grade is considered a very important factor.
For diamonds under one carat, each carat is divided into 100 points - similar to pennies in a pound. 0.50ct = 50 points.
Two diamonds of equal carat weight might vary greatly in value depending upon their cut, color and clarity. This is important because when mounted, one diamond may appear larger than the other, although they actually weigh the same. Because large diamonds are rare, they generally have a greater value per carat. For example, the price of a two-carat stone will be several times higher than four 50-pointers of equal quality.