|Excess Color Enhancers in Koi Feeds, And Pellet Size
Excess color enhancers
Use of excessive color enhancers in food can contribute to Yellowhead (which is fifty percent genetic, with food potentiation) Male fish of the Shiro class (and others) can have a yellow, or "bone" colored head. This is only worse on fish that get color enhancers. But remember, it's the maleness of the fish and it's genetics that set this in play, not the food.
Pink skin - This is an urban legend. I have never seen this even in fish offered crazy amounts of shrimp oil experimentally. However, it still exists in the literature. If I ever get a chance to make you a digital unretouched image of a case of this I will, and I will let you know.
An oddity about pellet size
Small fish need small pellets that they can wholly engulf, but they will spend time chasing the biggest pellets. It would be better for the fish if they were given a small pellet they could entirely engulf. They could fill their stomachs instead of scraping off a meal over a lengthy time.
Can small fish eat large pellet? Yes, but that is only by badgering the large pellet around the surface of the pond as it softens in the water, and eating off it like a giant peach.