Fancy vivid tends to be the most desirable, and is an ideal investment stone.

The other three Cs remain important. Clarity, cut and carat weight all affect value, but to a lesser extent than colour in fancy colour diamonds.

Demand for pink

The Argyle mines, the main producers of quality fancy pinks, face exhaustion and are set to close by 2020. Demand and prices are expected to surge once the supply is cut off.

Rio Tinto, which runs the Argyle mine, saw prices of its annual diamond tender triple from 2000 to 2015, increasing by an average of 15 per cent per year and reaching more than US$1 million per carat.

Last April, the record for the most expensive diamond sold at auction was set by the Pink Star, a 59.6ct internally flawless vivid pink. It was bought by Hong Kong jewellery retailer Chow Tai Fook for US$71.2 million and renamed the CTF Pink.

Rio Tinto’s tender this year is open for bidding, and includes a 3.14ct emerald-cut fancy vivid purplish pink christened the Argyle Alpha. It is the largest pink diamond in the tender’s 34-year history.

Investment or collector’s item?

According to the Diamond Investment & Intelligence Centre, red, blue, pink and yellow are colours for investment, whereas green, purple, violet and orange are colours for collectors. Although all fancy coloured diamonds are rare, that alone does not make them a good investment.

Green diamonds are rarer than blue ones, and second only to red diamonds. But finding a buyer may be more difficult, as demand is lower and potential buyers may not be willing to pay as much for a green diamond.

Growing appetite for green

Some investors are revisiting the idea of green being more of a collector’s colour. Lower prices for green diamonds may give a chance to buy low and sell high.

The price of greens has been rising. In 2014, the sale of the 5.51ct fancy deep blue-green Ocean Dream by Christie’s fetched US$1.56 million per carat. Most recently, Chow Tai Fook bought the 5.03ct Aurora Green for US$3.3 million per carat at Christie’s in 2016.

Conservative white

White diamonds are a more conservative investment, despite being lower than fancy colour diamonds. The record for a white diamond sold at auction is US$30.6 million for a 118.28ct D-colour flawless Type IIa oval diamond with excellent polish and symmetry.

The best white diamonds are colourless, which is reflected in their D-colour grade. The standard GIA grades for white diamond colours run from D to Z. Although D, E and F grades are generally colourless, the minute differences markedly affect the quality and value of a diamond.

Colourlessness is prized because colour absorbs light. This affects the diamond’s ability to allow light to pass through its prismatic depths and display the diamond’s characteristic fire. D-colour diamonds allow the most light to pass through.

Clarity impact

Among the four Cs, clarity is known as the one that provides the best chance for value – people often sacrifice a grade or two of clarity in favour of better cut, carat weight or colour, and subsequently pay less for what may still be considered a good stone.

Flaws in the highest four or even six grades of clarity are so small that they cannot be seen with the naked eye.

“Always look for stones that are colourless and of high clarities, with Gemmological Institute of America(GIA) certificates,” says J.J. Abram, director of Ronald Abram.

“Here in Asia, we tend to see our clients favour quality over size. It’s easy to become wowed by a large carat size, but what holds the most value in a diamond is colourless diamonds of higher clarities which are cut to the finest of proportions.”

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