Editing Diffuse reflection (section)

==Colored objects==
Up to this point white objects have been discussed, which do not absorb light. But the above scheme continues to be valid in the case that the material is absorbent. In this case, diffused rays will lose some wavelengths during their walk in the material, and will emerge colored.

Diffusion affects the color of objects in a substantial manner because it determines the average path of light in the material, and hence to which extent the various wavelengths are absorbed.<ref>Paul Kubelka, Franz Munk (1931), ''Ein Beitrag zur Optik der Farbanstriche'', Zeits. f. Techn. Physik, '''12''', 593–601, see [https://web.archive.org/web/20110717155703/http://web.eng.fiu.edu/~godavart/BME-Optics/Kubelka-Munk-Theory.pdf ''The Kubelka-Munk Theory of Reflectance''] {{webarchive|url=https://web.archive.org/web/20110717155703/http://web.eng.fiu.edu/~godavart/BME-Optics/Kubelka-Munk-Theory.pdf |date=2011-07-17 }}</ref> Red ink looks black when it stays in its bottle. Its vivid color is only perceived when it is placed on a scattering material (e.g. paper). This is so because light's path through the paper fibers (and through the ink) is only a fraction of millimeter long. However, light from the bottle has crossed several centimeters of ink and has been heavily absorbed, even in its red wavelengths.

And, when a colored object has both diffuse and specular reflection, usually only the diffuse component is colored. A cherry reflects diffusely red light, absorbs all other colors and has a specular reflection which is essentially white (if the incident light is white light). This is quite general, because, except for metals, the reflectivity of most materials depends on their [[refractive index]], which varies little with the wavelength (though it is this variation that causes the [[chromatic dispersion]] in a [[Prism (optics)|prism]]), so that all colors are reflected nearly with the same intensity.