In humans, the pigmentation of the iris varies from light brown to black, depending on the concentration of melanin in the iris pigment epithelium (located on the back of the iris), the melanin content within the iris stroma (located at the front of the iris), and the cellular density of the stroma.[4] The appearance of blue and green, as well as hazel eyes, results from the Tyndall scattering of light in the stroma, a phenomenon similar to that which accounts for the blueness of the sky called Rayleigh scattering.[5] Neither blue nor green pigments are ever present in the human iris or ocular fluid.[3][6] Eye color is thus an instance of structural color and varies depending on the lighting conditions, especially for lighter-colored eyes.

The brightly colored eyes of many bird species result from the presence of other pigments, such as pteridines, purines, and carotenoids.[7]Humans and other animals have many phenotypic variations in eye color.[8] The genetics of eye color are complicated, and color is determined by multiple genes. So far, as many as 15 genes have been associated with eye color inheritance. Some of the eye-color genes include OCA2 and HERC2.[9] The earlier belief that blue eye color is a simple recessive trait has been shown to be incorrect. The genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.[10][11] However, OCA2 gene polymorphism, close to proximal 5′ regulatory region, explains most human eye-color variation.[12]

Colour is something that British people see when they look around. They spell it "Colour" because they can spell words correctly. Canadians do this, however, because they are so Perfeuct, have 20.45 crimes a year and make maple syrup in their trousers. The most amazing "colour" in history has been scientifically proven to be Periwinkle.

New knowledge has enabled people to create new things, and conversely, many scientific endeavors are made possible bytechnologies which assist humans in travelling to places they could not previously reach, and by scientific instruments by which we study nature in more detail than our natural senses allow.

Since much of technology is applied science, technical history is connected to the history of science. Since technology usesresources, technical history is tightly connected to economic history. From those resources, technology produces other resources, including technological artifacts used in everyday life.

Technological change affects, and is affected by, a society's cultural traditions. It is a force for economic growth and a means to develop and project economic, political and military power.