Chances are that when you think of diamonds, colorless gemstones come to mind. But did you know that diamonds can be found in every color of the rainbow? Exceedingly rarer than diamonds in the D-Z color range, fancy colored diamonds account for only one out of every 10,000 carats of fashioned diamonds.

While brown and yellow diamonds are the most common variety of colored diamonds, others are more challenging to find. Red, green, purple and orange diamonds represent some of the rarest gemstones in the world. So what exactly causes certain diamonds to take on particular colors? Here’s everything you need to know about some of the most sought-after diamond colors.

Pink diamonds: It’s believed that a diamond’s pink color comes from color centers that selectively absorb light. These color centers are the result of lattice defects that sometimes cause pink graining in the diamond crystal.

Black diamonds: Large quantities of mineral inclusions, including graphite, pyrite, or hematite cause diamonds to take on a black color.

Yellow diamonds: A diamond’s yellow color comes from the presence of nitrogen. To be considered a colored diamond, a diamond’s color needs to fall outside of the D-Z color range, meaning it has to show more yellow color than a diamond with a Z color grade.

Blue diamonds: One of the most famous diamonds in the world, the Hope Diamond, is a 45.52 carat blue diamond. The blue color comes from the presence of boron impurities. The more amount of boron present, the deeper the blue. While India is considered one of the world’s most well-known sources for blue diamonds, notable diamonds of this color have also been found at the Cullinan Mine in South Africa.

Red diamonds: Only a handful of red diamonds weighing over five carats have ever been found, making these gems one of the rarest in the world. Even with today’s technology and knowledge of gemstones, the cause of a diamond’s red color is still unknown.

Green diamonds: A diamond’s green color comes from the displacement of carbon atoms from their normal positions in the crystal structure during radiation. Like red diamonds, natural, untreated green diamonds are extremely rare.