Read all about yellow diamonds 

Yellow in diamonds is caused by the presence of nitrogen within the stone that filters the blue/violet range of the visible light spectrum and reflects yellow. Since nitrogen is abundant in the Earth's crust, it can frequently find its way into the diamond during the growth process. Some diamonds have been found to contain as much as 1% nitrogen by weight. Most nitrogen is incorporated into a diamond as a single atom, however it can exist at a molecular level as well.

Nitrogen is so common in diamonds that the crystal itself is categorized based on the presence or lack of nitrogen. Common terms that we hear in the industry to describe diamonds are Type I or Type II. Type I diamonds contain nitrogen and account for 98% of all natural diamonds, while the much rarer Type II diamonds do not.

Estimates suggest that around 60% of all fancy color diamonds mined each year are fancy yellow. However they are still extremely rare. Approximately 1 out of every 10,000 carats mined each year is a fancy color diamond. This means that 1 carat out of every 16,600 carats mined is a fancy yellow. And according to a 2005 study by GIA, only 6% of stones graded on the fancy yellow spectrum were Fancy Vivid Yellow, the strongest and most valuable shade. This implies that it takes over 275,000 carats mined to produce just 1 carat of fancy vivid yellow diamonds. And of course large diamonds would be exceptionally rare, possibly found only a few times a year, if at all.