Albinism

Symptoms

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.

Animal Colouration

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.

Pigments

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:

• xanthophores (yellow): contain yellow pigments in the forms of carotenoids
• erythrophores (red): contain reddish pigments such as carotenoids and pteridine
• melanophores (black/brown): contain black and brown pigments such as the melanins
• cyanophores (blue): limited taxonomic range but found in some fish and amphibians

Structural Colours

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.

• iridophores (reflective/iridescent): sometimes called "guanophores", reflect light using plates of crystalline chemochromes made from guanine
• leucophores (reflective white): found in some fish, utilize crystalline purines (often guanine) to produce a reflective, shiny, white colour.

Plant Colouration

The primary function of pigments in plants is photosynthesis, which uses the green pigment chlorophyll along with several red and yellow pigments including porphyrins, carotenoids, anthocyanins and betalains.

Origin

Natural

Cycle

Chronic, Congenital

Rarity

Rare