If you're going to choose a diamond for a diamond engagement ring then you will need to consider the color of the stone you choose.

Usually thought to be as clear and bright as a mountain stream rippling in sunlight, diamonds come in almost every color imaginable, from pure white to palest gold to inky "black", the result of light refracting from a substance within the diamond.

For instance, the presence of nitrogen can produce yellow diamonds.

It has been estimated that there is one colored diamond for every 10,000 colorless or near-colorless diamonds found.

The most common color in diamonds is not white, but brown, and althoughused by the Romans in rings around 1AD to 3AD, they did not find favor withmodern connoisseurs and were consigned to industrial use. A notableexception is the 109.26ct Cross of Asia, cut so a Maltese Cross is visibleabove the table.

Then, in the 1980s, trash was turned into treasure when Australian marketers successfully promoted their brown gem-quality stones as "champagne" and "cognac" diamonds.

The auction of a red diamond in 1987,­ said to be bought by an agent for theSultan of Brunei for $US1 million, ­ quickened interest in colored diamonds.

After brown, yellow is the most common color. Found in abundance in Africa,they are known as Cape stones. The intense deep color of "canary" diamonds is the rarest of the yellows.

The 545.67ct Golden Jubilee is the world'slargest faceted diamond. Found in South Africa in 1986, it was presented tothe King of Thailand in 1997 to mark the 50th anniversary of his coronation.

The beautiful and extremely rare Blue Hope diamond.

Although quite rare, blue diamonds ­ (often grayish in color) ­ have been found in many parts of the world, including India, South Africa, Brazil, Indonesia and Australia. The most famous blue is the Hope diamond, with a reputation for bringing bad luck to its owner.

The Black Orloff from India and Black Star of Africa are among the few blackdiamonds not found in Brazil. Black diamonds are sometimes artificiallyproduced by irradiating low-clarity faceted diamonds to get a blue or green color so dark it appears black.

Green diamonds are not especially scarce but the green is almost invariablya very thin surface layer, lost when the stone is faceted. The Dresden Green, reputed to be of Indian origin, is now thought by some experts to be Brazilian. Whatever its origin, the 41ct almond-shaped gem is remarkable for its apple-green coloration throughout the stone.

Pink, red and purple diamonds are closely related. Western Australia's Argyle mine has become famous since the 1980s for producing high-quality pinks and reds, with a recent quotation of $US1.6 million for a top-grade pink diamond of just under one carat.

The Argyle mine has also produced some pure orange and violet diamonds, colorsunknown until found in Australia, although there are earlier reports of brownish- orange diamonds.

If you'd like to learn more about the qualities to look for when shopping for a diamond, read our comprehensive Diamond Buying Guide.