A crayon is a stick of colored wax, charcoal, chalk, or other material. A crayon made of oiled chalk is called an oil pastel; when made of pigment with a dry binder, it is simply a pastel. A grease pencil or china marker (UK chinagraph pencil) is made of colored hardened grease. Some fine arts companies such as Swiss Caran d'Ache manufacture water-soluble crayons.
Crayons, which are available at a range of price points, are easy to work with, often less messy than paints and markers, blunt (removing the risk of sharp points present when using a pencil or pen), usually non-toxic, and are available in a wide variety of colors. These characteristics make them particularly good instruments for teaching small children to draw in addition to being used widely by student and professional artists.
Color or colour (see spelling differences) is the visual perceptual property 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).