Color or colour (see spelling differences) is the visual perceptualproperty corresponding in humans to the categories called red, blue, yellow, green and others. Color derives from the spectrum of light (distribution of light power versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects, materials, light sources, etc., based on their physical properties such as light absorption, reflection, or emission spectra. By defining a color space, colors can be identified numerically by their coordinates.
Because perception of color stems from the varying spectral sensitivity of different types of cone cells in the retina to different parts of the spectrum, colors may be defined and quantified by the degree to which they stimulate these cells. These physical or physiological quantifications of color, however, do not fully explain the psychophysical perception of color appearance.
The science of color is sometimes called chromatics, chromatography, colorimetry, or simply color science. It includes the perception of color by the human eye and brain, the origin of color in materials, color theory in art, and the physics of electromagnetic radiation in the visible range (that is, what we commonly refer to simply as light).
Guanajuato is a city and municipality in central Mexico and the capital of the state of the same name. It is located in a narrow valley, which makes the streets of the city narrow and winding. Most are alleys that cars cannot pass through, and some are long sets of stairs up the mountainsides. Many of the city’s thoroughfares are partially or fully underground. The historic center of the city has numerous small plazas and colonial-era mansions, churches and civil constructions built using pink or green sandstone.
The origin and growth of the city resulted from the discovery of mines in the mountains surrounding it. The mines were so rich that the city was one of the most influential during the colonial period. One of the mines, La Valenciana, accounted for two-thirds of the world’s silver production at the height of its production.
The city is home to the Mummy Museum, which contains naturally mummified bodies that were found in the municipal cemetery between the mid 19th and 20th centuries. It is also home to the Festival Internacional Cervantino, which invites artists and performers from all over the world as well as Mexico. The city was also the site of the first battle of the Mexican War of Independence between insurgent and royalist troops at the Alhóndiga de Granaditas. The city was named a World Heritage Site in 1988.