Goldfish, like other cold-blooded animals, have pigmented cells called chromatophores. Inside the chromatophores are chromatosomes, which are the organelles that contain the pigment. Chromatosomes can absorb or reflect light. The color of a fish is dictated by the type of chromatosomes present in its cells, how many chromatosomes there are, and where the chromatosomes are located in the cell; these, in short, control which chromatosomes absorb light and which reflect it, thus influencing the color we see when we look at fish. Chromatophores can change color in two ways: by spreading chromatosomes within cells, making the color more obvious to the eye; or by chromatosomes changing color, causing a visual color difference throughout the organism. When outdoors and exposed to natural sunlight, fish absorb ultraviolet light (UVA and UVB) from the sun. UVA and UVB rays are high-energy light and can be destructive to other animals, but pigments protect fish from this, and ultraviolet light is actually needed by fish because it's what activates chromatophores to produce more pigment molecules . Essentially, UVA and UVB rays hitting the pigments in fish trigger the production of more pigments. Different wavelengths of light determine what colors we see in fish and other organisms. For example, seasonal changes that affect the length of daylight cause many species in nature to put on their extreme reproductive garb. Scientific studies show numerous reports of fish losing color after going blind, an observation that would have some implications for fish kept in the dark. Lighting in goldfish tanks can alter the pigment of goldfish in various ways. The center...... of the paper...... and the goldfish will appear lighter in color. In addition to the amount of pigment produced, UVA and UVB light also affects the density of the pigments in the cell, which in turn also impacts the color of the fish. This happens quickly, even as quickly as (as stated in one of the sources) "you may notice that when you turn on the aquarium light in the morning, the fish may appear paler, but will appear more vibrant later in the day." artificial and the type of food given to a fish can also affect the fish's pigmentation and coloration. The longer a fish is not exposed to sunlight, the type of artificial light it receives and the type of food it eats will affect the coloration of the fish. When the chromatophores in the fish die, they will not be replaced by new ones, due to lack of sunlight, and the color of the fish will change.