Hue in the context of "Darkness"

Color (or colour in Commonwealth English) is the visual perception produced by the activation of the different types of cone cells in the eye caused by light. Though color is not an inherent property of matter, color perception is related to an object's light absorption, emission, reflection and transmission. For most humans, visible wavelengths of light are the ones perceived in the visible light spectrum, with three types of cone cells (trichromacy). Other animals may have a different number of cone cell types or have eyes sensitive to different wavelengths, such as bees that can distinguish ultraviolet, and thus have a different color sensitivity range. Animal perception of color originates from different light wavelength or spectral sensitivity in cone cell types, which is then processed by the brain.

Colors have perceived properties such as hue, colorfulness, and lightness. Colors can also be additively mixed (mixing light) or subtractively mixed (mixing pigments). If one color is mixed in the right proportions, because of metamerism, they may look the same as another stimulus with a different reflection or emission spectrum. For convenience, colors can be organized in a color space, which when being abstracted as a mathematical color model can assign each region of color with a corresponding set of numbers. As such, color spaces are an essential tool for color reproduction in print, photography, computer monitors, and television. Some of the most well-known color models and color spaces are RGB, CMYK, HSL/HSV, CIE Lab, and YCbCr/YUV.

In mathematics, analytic number theory is a branch of number theory that uses methods from mathematical analysis to solve problems about the integers. It is often said to have begun with Peter Gustav Lejeune Dirichlet's 1837 introduction of Dirichlet L-functions to give the first proof of Dirichlet's theorem on arithmetic progressions. It is well known for its results on prime numbers (involving the Prime Number Theorem and Riemann zeta function) and additive number theory (such as the Goldbach conjecture and Waring's problem).

Yarn is a long continuous length of interlocked fibres, used in sewing, crocheting, knitting, weaving, embroidery, ropemaking, and the production of textiles. Thread is a type of yarn intended for sewing by hand or machine. Modern manufactured sewing threads may be finished with wax or other lubricants to withstand the stresses involved in sewing. Embroidery threads are yarns specifically designed for needlework. Yarn can be made of a number of natural or synthetic materials, and comes in a variety of colors and thicknesses (referred to as "weights"). Although yarn may be dyed different colours, most yarns are solid coloured with a uniform hue.

Lightness is a visual perception of the luminance ${\displaystyle (L)}$ of an object. It is often judged relative to a similarly lit object. In colorimetry and color appearance models, lightness is a prediction of how an illuminated color will appear to a standard observer. While luminance is a linear measurement of light, lightness is a linear prediction of the human perception of that light.

This distinction is meaningful because human vision's lightness perception is non-linear relative to light. Doubling the quantity of light does not result in a doubling in perceived lightness, only a modest increase.

Line art or line drawing is any image that consists of distinct straight lines or curved lines placed against a background (usually plain). Two-dimensional or three-dimensional objects are often represented through shade (darkness) or hue (color). Line art can use lines of different colors, although line art is usually monochromatic.

Several techniques used in printmaking largely or entirely use lines, such as engraving, etching and woodcut, and drawings with pen or pencil may be made up of lines.

Monochrome photography is photography where each position on an image can record and show a different amount of light (value), but not a different color (hue). The majority of monochrome photographs produced today are black-and-white, either from a gelatin silver process, or as digital photography. Other hues besides grey can be used to create monochrome photography, but brown and sepia tones are the result of older processes like the albumen print, and cyan tones are the product of cyanotype prints.

As monochrome photography provides an inherently less complete reproduction than color photography, it is mostly used for artistic purposes and certain technical imaging applications.

Coralline algae are red algae in the order Corallinales, characterized by a thallus containing calcareous deposits within its cell walls, giving it hardness. The colors of these algae are typically some hue of pink, or another shade of red, but some species can be purple, yellow, blue, white, or gray-green. Typically, these algae grow in a crustose manner (encrusting rocks and other hardscape); in the intertidal zone of rocky shorelines, and within coral reefs, these algae appear as an abundance of colorful patches on rock surfaces. Unattached specimens (maerl, rhodoliths) may form relatively smooth compact balls, or forming warty to fruticose thalli.

The red algae belong to the division Rhodophyta, within which the coralline algae form the order Corallinales. There are over 1600 described species of nongeniculate coralline algae. The corallines are presently grouped into two families on the basis of their reproductive structures. Most are marine, though one species lives in freshwater; Pneophyllum cetinaensis.

Azure is the color between cyan and blue on the spectrum of visible light. It is often described as the color of the sky on a clear day.

On the RGB color wheel, "azure" (hexadecimal #0080FF) is defined as the color at 210 degrees, i.e., the hue halfway between blue and cyan. In the RGB color model, used to create all the colors on a television or computer screen, azure is created by adding a 50% of green light to a 100% of blue light.