Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and red or pink or purple or blue eyes. Individuals with the condition are referred to as albinos.

Varied use and interpretation of the terms mean that written reports of albinistic animals can be difficult to verify. Albinism can reduce the survivability of an animal; for example, it has been suggested that albino alligators have an average survival span of only 24 years due to the lack of protection from UV radiation and their lack of camouflage to avoid predators. It is a common misconception that all albino animals have characteristic pink or red or violet eyes (resulting from the lack of pigment in the iris allowing the blood vessels of the retina to be visible); this is not the case for some forms of albinism. Familiar albino animals include in-bred strains of laboratory animals (rats, mice and rabbits), but populations of naturally occurring albino animals exist in the wild, e.g., Mexican cave tetra. Albinism is a well-recognized phenomenon in molluscs, both in the shell and in the soft parts. By definition albinism is a genetic condition, however a similar coloration could be caused by diet, living conditions, age, disease, or injury.

Oculocutaneous albinism (OCA) is a clearly defined set of seven types of genetic mutations which reduce or completely prevent the synthesis of eumelanin or pheomelanin, resulting in reduced pigmentation. Type I oculocutaneous albinism (OCA1a) is the form most commonly recognised as 'albino' as this results in a complete absence of melanin in the skin, hair/fur/feathers, and pink pupils, however this has led many to assume that all albinos are pure white with pink pupils, which is not the case.

In plants, albinism is characterised by partial or complete loss of chlorophyll pigments and incomplete differentiation of chloroplast membranes. Albinism in plants interferes with photosynthesis, which can reduce survivability. Some plant variations may have white flowers or other parts. However, these plants are not totally devoid of chlorophyll. Terms associated with this phenomenon are "hypochromia" and "albiflora".

Biological pigments are substances produced by living organisms that have a colour resulting from selective colour absorption. What is perceived as a plant or animal's "colour" is the wavelengths of light that are not absorbed by the pigment, but instead are reflected. Biological pigments include plant pigments and flower pigments.

Animals can appear coloured due to two mechanisms, pigments and structural colours. Animals may have both biological pigments and structural colours, for example, some butterflies with white wings.

Many animal body-parts, such as skin, eyes, feathers, fur, hair, scales and cuticles, contain pigments in specialized cells called chromatophores. These cells are found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and birds, in contrast, have a class of cells called melanocytes for colouration. The term chromatophore can also refer to coloured, membrane-associated vesicles found in some forms of photosynthetic bacteria. Chromatophores are largely responsible for generating skin and eye colour in poikilothermic animals and are generated in the neural crest during embryonic development. Mature chromatophores are grouped into subclasses based on their colour under white light:

Animals can also appear coloured due to structural colour, the result of coherent scattering perceived as iridescence. The structures themselves are colourless. Light typically passes through multiple layers and is reflected more than once. The multiple reflections compound one another and intensify the colours. Structural colour differs according to the observer's position whereas pigments appear the same regardless of the angle-of-view. Animals that show iridescence include mother of pearl seashells, fish, and peacocks. These are just a few examples of animals with this quality, but it is most pronounced in the butterfly family.