Then there are collectors who look for rare gems of unparalleled color and size, such as the 407.48-carat fancy brownish-yellow kite-shaped Incomparable Diamond. It was the largest of the 15 stones cut from an 890-carat rough found in the early 1980s by a young girl in the Mbuji-Mayi district of the Democratic Republic of Congo. It is the largest flawless diamond ever cut.

The demand for colored diamonds has increased over the past several years. "The production of natural colored diamonds coming out of the earth has not changed dramatically in the last 15 to 20 years, but the amount of wealth has changed, spurring a demand, which has driven prices up," says Robert May, executive director of the Natural Color Diamond Association. Curiel is more specific: "Middle Eastern clients are great collectors of colored diamonds in large sizes, while Asia is the prime market for these gems, but in small sizes." "There is a major increase in price mostly for reds, blues and pinks," says Lior Levin, marketing director for the Geneva-based Steinmetz Diamond Group.

Pink diamonds come primarily from the Argyle mine in Australia, in operation since 1985. "The Argyle has acquired the honor of being the only mine in the world that produces a consistent quality of rare pink diamonds," says Jean-Marc Lieberherr, general manager of Rio Tinto Diamonds, which owns the Argyle mine. "The collectability of pink diamonds is unprecedented, and the desire to own the rarest has sent prices skyrocketing. With the Argyle mine forecast to close in 2018, the exclusivity and image of pink diamonds as a key investment option has been enhanced." Each year, the mine releases 60 to 65 of the rarest pink diamonds from the mine at the Argyle Pink Diamond Tender, which are restricted to about 100 clients who leave bids. "Known as the Argyle Signature Stones, these rare gems have an unparalleled depth of color and quality."

Every colored diamond must have a certificate attesting that it is a natural stone, not one treated to enhance its color. The laboratories offering certificates are the GIA (Gemological Institute of America), the AGS (American Gem Society), the IGI (International Gemological Institute) and the EGL (European Gemological Lab). A certified lab will be able to tell whether a diamond has been treated to modify its color or has been made synthetically. A lesser-value diamond can be irradiated or a coating can be applied onto the pavilion of the stone to enhance its color. Synthetic diamonds are made in either of two methods. The first is High Pressure High Temperature (HPHT), which mimics the natural formation of colored diamonds in the earth. Gemesis in Sarasota, Florida, grows such diamonds. The second, Chemical Vapor Deposition (CVD), is a process by Apollo Diamond in Boston, Massachusetts. According to Matthew Hall, Manager of Identification at the GIA in New York, "The GIA can detect the vast majority of diamonds that are treated." Their mission is to stay on top of trends and treatments.

In the last five years, numerous designers and retailers have been utilizing colored diamonds in their designs. For some, the diamond is the focal point of the design. When Christian Tse, a jewelry designer from California, first saw a 23-carat fancy pink diamond, he knew within five minutes that he had to buy it. "I have seen many other pink diamonds, but this one was saturated and had all the right proportions," he says. "This stone spoke to me." He set it into the pendant of a necklace within a colorless diamond ribbon-like mounting. James de Givenchy of the New York–based jewelry design studio Taffin chose a 2.75-carat fancy dark grey/green/yellow diamond to set into a ring mounting made of steel. This is not just any colored diamond, but a chameleon that changes color depending on the light.

Artist Daniel Brush from New York City is fascinated by jewelry and creates designs that are decidedly not mainstream. Instead of using traditional metals such as gold and platinum, he prefers nonprecious materials such as Bakelite. His line of jewelry, the Menagerie Magnetique, depicts animals studded with colored diamonds; one example is a poodle with orange and yellow diamonds. "Colored diamonds are extremely allusive, charming and dreamy," says Brush. "Perhaps because of the way the saturation is dispersed, it becomes a description beyond color or mood."

Michelle Ong, who designs for Carnet in Hong Kong, created a pair of ear pendants in the form of grape bunches. The grapes are made of briolette-cut diamonds, one bunch white, the other black, with the leaves in opposing colors. Neil Lane, a celebrity jeweler from Los Angeles, was inspired by pebbles that he collected at the beach as a child when designing a bangle bracelet with faceted rough-cut colored diamonds in many different shapes.

"The house of Cartier has a long history of using the finest colored diamonds to create some of the most exquisite jewelry the world has seen—from the legendary 45.5-carat Hope diamond to the most astounding necklace ever created by Cartier for the Maharajah of Patiala featuring the famed 234.69-carat yellow diamond," says Frédéric de Narp, president and CEO of Cartier North America. Today, colored diamonds continue to grace Cartier’s collections, including the Inde Mystérieuse Bengal Tiger ring with yellow diamonds, the design rooted in India and based on the historic relationship between Cartier and the maharajahs.