Blue is one of the three primary colours in the RYB colour model, as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when observing light with a dominant wavelength between approximately 450 and 495 nanometres. Most blues contain a slight mixture of other colours; azure contains some green, while ultramarine contains some violet. The clear daytime sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering. An optical effect called Tyndall effect explains blue eyes. Distant objects appear more blue because of another optical effect called aerial perspective.
Violet is the color of light at the short wavelength end of the visible spectrum, between blue and invisible ultraviolet. It is one of the seven colors that Isaac Newton labeled when dividing the spectrum of visible light in 1672. Violet light has a wavelength between approximately 380 and 435 nanometers. The color's name is derived from the violet flower.
Georg Brandt was a Swedish chemist and mineralogist who discovered cobalt. He was the first person to discover a metal unknown in ancient times. He is also known for exposing fraudulent alchemists operating during his lifetime.
Umber is a natural brown earth pigment that contains iron oxide and manganese oxide. In its natural form, it is called raw umber. When calcined, the color becomes warmer and it becomes known as burnt umber.
Navy blue is a very dark shade of the color blue.
Powder blue is a pale shade of blue. As with most colours, there is no absolute definition of its exact hue. Originally, powder blue, in the 1650s, was powdered smalt used in laundering and dyeing applications, and it then came to be used as a colour name from 1894.
Cerulean, also spelled caerulean, is a shade of blue ranging between azure and a darker sky blue.
Cobalt blue is a blue pigment made by sintering cobalt(II) oxide with aluminum(III) oxide (alumina) at 1200 °C. Chemically, cobalt blue pigment is cobalt(II) oxide-aluminium oxide, or cobalt(II) aluminate, CoAl2O4. Cobalt blue is lighter and less intense than the (iron-cyanide based) pigment Prussian blue. It is extremely stable and historically has been used as a coloring agent in ceramics (especially Chinese porcelain), jewelry, and paint. Transparent glasses are tinted with the silica-based cobalt pigment smalt.
Royal blue is a deep and vivid shade of blue. It is said to have been created by clothiers in Rode, Somerset, a consortium of whom won a competition to make a dress for Queen Charlotte, consort of King George III.
Cobalt glass—known as "smalt" when ground as a pigment—is a deep blue coloured glass prepared by including a cobalt compound, typically cobalt oxide or cobalt carbonate, in a glass melt. Cobalt is a very intense colouring agent and very little is required to show a noticeable amount of colour.
The color of water varies with the ambient conditions in which that water is present. While relatively small quantities of water appear to be colorless, pure water has a slight turquoise color that becomes deeper as the thickness of the observed sample increases. The hue of water is an intrinsic property and is caused by selective absorption and scattering of white light. Dissolved elements or suspended impurities may give water a different color.
A humidity indicator card (HIC) is a card on which a moisture-sensitive chemical is impregnated such that it will change color when the indicated relative humidity is exceeded. This has usually been a blotting paper impregnated with cobalt(II) chloride base; Less toxic alternatives include other chemicals such as cobalt-free chloride base and special plastic films.
Cobalt(II) thiocyanate is an inorganic compound with the formula Co(SCN)2. It is a layered coordination complex and its trihydrate Co(SCN)2(H2O)3 is used in the cobalt thiocyanate test (or Scott test) for detecting cocaine. The test has been responsible for widespread false positives and false convictions.
The Platinum-Cobalt Scale is a color scale that was introduced in 1892 by chemist Allen Hazen (1869–1930). The index was developed as a way to evaluate pollution levels in waste water. It has since expanded to a common method of comparison of the intensity of yellow-tinted samples. It is specific to the color yellow and is based on dilutions of a 500 ppm platinum cobalt solution. The colour produced by one milligram of platinum cobalt dissolved in one liter of water is fixed as one unit of colour in platinum-cobalt scale. The ASTM has detailed description and procedures in ASTM Designation D1209, "Standard Test Method for Color of Clear Liquids ".
A color chart or color reference card is a flat, physical object that has many different color samples present. They can be available as a single-page chart, or in the form of swatchbooks or color-matching fans.
Livid is a medium bluish-gray color. This color name comes from the Latin color term lividus meaning "'a dull leaden-blue color', and also used to describe the color of contused flesh, leading to the English expression 'black and blue'". The first recorded use of livid as a color name in English was in 1622.
Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.
Varieties of the color blue may differ in hue, chroma, or lightness, or in two or three of these qualities. Variations in value are also called tints and shades, a tint being a blue or other hue mixed with white, a shade being mixed with black. A large selection of these colors is shown below.
The color cyan, a greenish-blue, has notable tints and shades. It is one of the subtractive primary colors along with magenta, and yellow.
Color coordinates
