Diamonds in the normal colour range are colourless through light yellow and are described using the industry’s D-to-Z color-grading scale. Fancy colour diamonds, on the other hand, are yellow and brown diamonds that exhibit colour beyond the Z range, or diamonds that exhibit any other colour face-up. These rare specimens come in every colour of the spectrum, including, most importantly, blue, green, pink, and red.
Gem diamonds in the D-to-Z range usually decrease in value as the colour becomes more obvious. Just the opposite happens with fancy colour diamonds: Their value generally increases with the strength and purity of the colour. Large, vivid fancy colour diamonds are extremely rare and very valuable. However, many fancy diamond colours are muted rather than pure and strong.
The yellow coloration in diamonds is primarily caused by nitrogen impurities within the diamond’s crystal structure, which absorb blue light and give the stone a warmer appearance.
Yellow diamonds are much rarer than the classic clear diamonds, but they are more often seen than the other fancy diamond colours. Yellow diamonds are sometimes called canary diamonds after the bird’s brilliant yellow plumage.
Yellow diamonds were scarce until the large diamond mines of South Africa were opened up in the 1860s. Although yellow coloured diamonds are less commonly found than colourless or white diamonds, they are the most frequently seen of the fancy coloured diamonds. Diamond experts suggest that yellow diamonds account for around 60% of all coloured diamonds. The number of yellow diamonds, in comparison to all diamonds, is tiny at about 1 in 5000 making them, in real terms, very rare.