What is the link between light and colour?
Electromagnetic radiation, or light, is characterized by its wavelength (or frequency) and its intensity. The human eye can discern only those wavelengths within the so-called visible spectrum (approximately from 380 nm to 740 nm); thus these wavelengths are known as "visible light". Color results from the spectrum of light (distribution of light energy versus wavelength) interacting with materials in the world, including the eye. Each wavelength represents a unique color.
Most light sources emit light at many different wavelengths; a source's spectrum is a distribution showing its intensity at each wavelength. Red is represented by wavelengths ~740-635 nm; orange by ~635-590 nm; yellow by ~590-560 nm; green by ~560-490 nm; blue by 490-450 nm; and violet by 450-380 nm. In addition, wavelengths may be superimposed on one another, such that red and yellow radiation will appear orange, for example. The human eye is most adept at picking up green wavelengths, and green colors appear the brightest.
Objects appear to be a certain color because they absorb light of all other colors except that color, or a spectrum of wavelengths that appear to be that color to the eye. An object that scatters all light wavelengths equally appears white. This is why white light seperates into the spectrum of light listed above when it passes through a prism, or forms a rainbow.