The ones that use hormones are primarily used by breeders/fish farmers, and these foods are generally not open to sale over the counter to the general public. However, needless to say you should always look at the ingredients on the back of the food container, both with people foods and animal/fish foods. A lot of pet foods, particually fish foods, contain ash which is used to bulk out the food and holds no health bennefets/nutritional value to the fish/animal. Generally speaking, the more ash the food contains the lower the quality of the food product is.
Most normal and available "color enhancing" foods just contain natural ingredients like spirulina algae (high in vitamins/minerals) and carotenoids. Krill is also good for bring out color in fish. But generally speaking, these foods won't do much for the fish if it is stressed, sick, under or over-fed or has a poor or inadequate diet etc. So to get the most out of your fishes colour, you should attend to the needs of not just the fishes diet but also its environment and the stocking of the environment as well.
Stale fish food loses its vitamins/nutritional value as it gets older, and flake foods are particually prone to going stale or moldy or both. Some fish food packets contain a dry tab thing which absorbs moisture and helps prevent the food from going stale. You can also buy vitamin/mineral supliments specially designed for aquariums, these supliments can either be directly added to the water or sprayed on the fishes food to boost its nutritional value.
Frozen, fresh or live foods are more healthy for fish than dried foods, so if you can, you should try and get some frozen/fresh or live foods into your fishes diet whenever you can- also don't forget to attend to your fishes veg needs, as the majority of fish are omnivores or need at least a certain amount of veg in their diet every now and then.
