The first two words in the name of every koi indicate the colouring of the koi. Every Koi is differentiated by a pattern created by those two colours. There are 30 primary colours and 30 secondary colours. Certain colours and colour combinations are rarer than others. The rarest colour combination for every breed is the Black Night.
The Koi Log, accessed through the menu, records all koi owned at any time, their age in days, and their rarity ranking out of 28,800.
There are 28,800 possible breed and colour combinations, out of which there are 900 colour combinations for each breed. Some colour combinations are higher in ranking than others of rarer breeds: for example, although the Cosomi is a rarer breed than the Bekko, the Black Night Bekko is higher ranked (26,617) than the Cream Ash Cosomi (27,324).
The 30 primary colors are as follows, from most common to rarest.
The 30 secondary colors are as follows, from most common to rarest.