Goldfish are naturally white due to their pigment. However, if you want them to be any other color it’s necessary for them to receive some UV rays from the sun or artificial light sources such as an aquarium fluorescent bulb and plant-based stimulant lights. When exposed to too much sunlight they usually respond by changing colors quickly because this is how goldfish show off in order to get around so easily being camouflaged on land where predators can grab hold easier than underwater!