It is really form the original red forms that the koi story starts to take shape. From the original red form the white koi was produced, and crossbreeding the two forms resulted in red and white koi. The first red koi were called Hoo-kazuki, while the first white and red were known as Hara-aka, which means red belly. Further crossbreeding produced the red-cheeked koi (hoo-aka) and so slowly but surely, the dedicated breeders of the region started to gain knowledge in how to maintain mutational colours. Thought they had no idea of genetics at the time, they simply experimented with matings.
The story is still the same today because the genetics of colour transmission in koi is so complicated, and even if it is applied, it is extremely difficult to predict results.