Yellow diamonds are an extremely rare variety of diamond called fancy coloured. On average only 1 in 10,000 diamonds are found naturally like this. Yellow diamonds’ unique colour comes from the presence of nitrogen. The nitrogen molecules absorb blue light, making the stone a yellow shade. Depending on the amount of nitrogen, a yellow diamond can range from lighter to darker in colour. Officially, canary diamonds are simply fancy yellow diamonds, graded anywhere from fancy intense to fancy vivid on the GIA colour scale. Canary Yellow is a casual term used for yellow diamonds with a pure yellow colour, not an official term. Just like white diamonds there is a chart for grading the colour of these stones. However, they follow and entirely different system than regular diamonds. The GIA colour grading scale for yellow diamonds is: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Vivid, Fancy Deep or Fancy Dark.

Citation: https://www.diamonds.pro/education/canary-yellow/