What is commonly referred to as "koi" is a short term for the Japanese word nishikigoi, that literally means brocaded (or adorned) carp. A domesticated version of the common carp, koi fish is usually seen in outdoor ponds or water gardens where their wide varieties of colors are showcased. There are many different types of koi available and koi hobbyists are continuously developing new types featuring a vast array of beautiful colors and patterns.
One of the most popular types is the Gosanke, which is a broad term used for three common types of koi: kohaku, sanke, and showa. The three basic colors than can be found on this type are hi or the red color patterns, shiroji or the white color (often seen as a background color), and sumi which is the black color pattern.
Kohaku is the most common type among the three. Its distinguishing feature is the white background with red markings or hi that are all over the body. These color patterns should be uniform in depth and have well-defined edges. Koi enthusiasts often use this type in crossbreeding with other types of koi like Doitsu or Ochiba.
Sanke, also known as Sanshoku, have features very similar to Kohaku. However, in addition to the hi or red patterns, this type also has sumi or black markings around the body. Keep in mind that sumi on Sanke should never be seen on the head. Showa is also tri-colored koi like Sanke but sumi is usually seen on the head of a Showa. It is often described as a black koi with shiroji or white patterns and deep red markings around the body.
Another commonly seen type of nishikigoi is the Bekko. Its name is a derivative of the Japanese word meaning "tortoise shell", which also has three different varieties under its name. Shiro Bekko is probably the only one among the three that is widely known. Its simplistic beauty is characterized by shiroji or a white background, with sumi (black) markings on their body that are usually located on the top side creating a lateral line. Always remember that any hi or red marking on the koi would automatically classify them as Sanke.
Aka Bekko is a type of koi with a scarlet red body overlain with sumi or black color patterns and white or sometimes clear finnage - in some cases, hi can be seen on the finnage as blotches and not the usual stripes. Ki Bekko is considered to be the rarest among the three variations. They are seen with a bright yellow body with patterns of sumi on top of the yellow color. Its name is based on the color of the fish Ki, which is a Japanese word for yellow.
GinRin is another one of the popular types of Koi. First developed in 1929 by a koi enthusiast, this type of Japanese carp was initially called Gingoke. The scales of this koi are a bit different from the usual metallic koi types. Scales of GinRin produces a glimmering effect that reflects the color of the pigment that overlays the silver area of the scale. Its name is derived from the colors that are seen which are silver (Gin) and gold (Kin) - GinRin is a short name for Kin-Gin-Rin.