- Genetics: Koi are genetically predisposed to certain colours and patterns. Some koi may have a dominant colour gene that will express itself more strongly, while others may have recessive colour genes that will only express themselves if both parents carry the same gene.
- Diet: The food that a koi eats can also affect its colour. Koi that are fed a diet rich in carotenoids, such as those found in carrots and peppers, will develop a more orange or red colour. Conversely, koi that are fed a diet lacking in carotenoids will develop a more pale or washed-out colour.
- Temperature: Water temperature can also affect the colour of koi. Koi that are kept in warm water will develop a more vibrant colour, while koi that are kept in cold water will develop a more dull or muted colour.
- Stress: Stress can also cause koi to change colour. Koi that are stressed may develop a darker colour or may lose their colour altogether.
It is important to note that not all koi will change colour. Some koi may maintain their original colour throughout their lives, while others may change colour multiple times.