Koi cannot produce the colours themselves and need carotenoids( colourants) in their diet to help produce the colour. Hikari Gold and Saki Colour both contain Astaxanthin, a powerful colour enhancer, which will brighten up the orange/ red on your koi without affecting the whites. Poorer quality foods may make the whites appear creamy. Feed above 16C for best results.
Simply written and easy to understand. Koi for Dummies is your useful guide to koi husbandry. How to get the best out of your hobby and fish!