Although many people might think Koi are simply large goldfish, owners know they have their own special dietary needs. For optimal color and health, feed them special Koi foods rather than goldfish food, or even standard pond foods. Here are the Koi foods I would choose.
1. Sho Koi Impact
Sho Koi Impact contains dried bugs, pupae, larvae, air-dried krill and air dried fresh water shrimp, to enhance colors in Koi naturally. Highly digestible and long floating. A bit more expensive than standard staple foods, but worth the extra cost. 
2. Hikari Koi Gold
Formulated with color-enhancing carotenoid Hikari Koi Gold will bring out the vibrant colors of your Koi. Comes in various sizes of resealable pouches that store well on the shelf.
3. Tetra Pond Growth Food for Koi
Teta Pond Growth is an excellent food to offer Koi during the warmer months when they experience growth spurts. Well balanced with high protein and the A vitamins and minerals necessary for optimal growth.4. Wardley Total Growth Koi Food
Wardley makes a good quality floating pellet food designed with extra vitamins that are needed during growth periods. The pellets are multi-sized to appeal to a variety of sizes of Koi, and come packaged in a sturdy resealable pouch.5. Azoo Color Koi Food
Great for enhancing the beautiful coloration of your Koi. Also provides balanced nutrition to boost immunity and reduce the amount of waste in your pond. Available in small and bulk quantities.