There are 13 recognized categories of Koi coloration. These are based on the marking patterns, colors and/or scale types. Koi do not breed true to color categories so it's a crap shoot as to whether that expensive breeder will produce great offspring.

Lots of Koi groups and breeders are getting into the action and because of this more and more new combinations and types of Koi are becoming popular. Eventually the most popular ones will become the next categories.

Asagi - Asagi means pale blue in Japanese so this is a Koi fish type that bears pale blue color and has orange belly. It also has regular scales and net pattern on the back.

Bekko - You will see Bekko in white, yellow or red colors and have black markings. Bekko means Tortoise in Japanese and the markings on the fish reflect those shapes.

Hakarimono (Ogon) - Metallic Koi are becoming very popular in the states. This type of Koi bears no markings and is single-colored metallic.

Hariwake - Another popular metallic Koi. This one has two colors and a Doitsu scales pattern which is either no scales at all or a single line of large dark mirrored scales.

Karasugoi - A Black Koi fish that has an orange or white belly.

Kohaku - This is the koi you usually see advertised. One of the first true breeds, this Koi is white with red markings.

Koromo - Koi fish with red markings on its white body. It is "robed" with scales whose outline bears different colors. Koromo means, "robed" in Japanese.

Matsuba - The "pine cone Koi". A fish that has scales patterned as pine cone. Single colored with darker scales.

Sanke - Another very famous color pattern that you see advertised. A white Koi fish with black and red markings. No black on the head of the fish though.

Showa - A black Koi with white and red markings.

Shusui - Similar to the Asagi in that it is blue with an orange belly. It has a large line of scales similar to the Doitsu scale pattern with dark blue color running down its back.

Tancho - A Koi fish with red spots on the head. The spots may be triangle or circular in shape. Here the shape and size of the spots determine the class.

Utsuri - A Koi fish with black stripes and has yellow, red or white markings. Similar to a Showa Koi.

You will find at Koi auctions subcategories of the main ones being listed using combinations of the main ones. Can be confusing at first but once you understand the basic 13 you will get the hang of the combo's.

The Koi Club of the Air have a great image that shows the main types plus some fo the more popular subcategories.