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Blue facts for kids

Kids Encyclopedia Facts
This box shows the color blue.
Mountain Bluebird
The Earth seen from Apollo 17
The famous Blue Marble picture of Earth, taken by NASA's Apollo 17

Blue is one of the colors of the rainbow that people can see. It is one of the three primary colors, along with red and yellow. It has the shortest wavelength of these colors (about 470 nanometers).

Blue is the color of the Earth's sky and sea. Earth looks blue when seen from outer space by astronauts.

Blue is a color used to show coldness. It is also one of the colors your lips can turn if you are chilly.

Blue is the color of a bluebird. A blue jay is the color blue.

Comparison of blue, indigo, violet, and purple

Name Color HEX Code Red Green Blue Hue Sat Lum
Blue #0000FF 0 0 255 240° 100% 50%
Indigo (Electric Indigo) #6F00FF 111 0 255 266° 100% 50%
Violet (Color Wheel) (Near Violet) #7F00FF 127 0 255 274° 100% 50%
Violet (Electric Violet) (Middle Violet) #8F00FF 143 0 255 270° 100% 50%
Vivid Violet (Extreme Violet) #9F00FF 159 0 255 277° 100% 50%
Purple #800080 128 0 128 300° 100% 50%

Tones of blue color comparison chart

Azure Mist (web color: Azure) (Hex: #F0FFFF) (RGB: 240, 255, 255)
Alice Blue (web color) (Hex: #F0F8FF) (RGB: 240, 248, 255)
Bubbles ( Color List) (Hex: #E7FEFF) (RGB: 231, 254, 255)
Light Cyan (Hex: #E0FFFF) (RGB: 244, 255, 255)
Lavender Mist (web color: Lavender) (Hex: #E6E6FA) (RGB: 230, 230, 250)
Periwinkle (Lavender Blue) (Pastel Indigo) (Hex: #CCCCFF) (RGB: 204, 204, 255)
Powder Blue (web color) (Hex: #B0E0E6) (RGB: 176, 224, 230)
Light Blue (Hex: #ADD8E6) (RGB: 173, 216, 230)
Ultra Blue (Crayola: Blizzard Blue) (Hex: #ACE5EE) (RGB: 172, 229, 238)
Baby Blue (Hex: 89CFF0) (RGB: 137, 207, 240)
Light Sky Blue (web color) (Hex: #87CEFA) (RGB: 135, 196, 250)
Sky Blue (web color) (Hex: #87CEEB) (RGB: 135, 206, 235)
Light Cornflower Blue (Crayola: Cornflower) (Hex: #93CCEA) (RGB: 147, 204, 234)
Medium Sky Blue (Crayola: Sky Blue) (Hex: #76D7EA) (RGB: 118, 215, 234)
Aquamarine Blue (Crayola: Aquamarine) (Hex: #71D9E2) (RGB: 113, 217, 226)
Aquamarine (web color) (Hex: #7FFFD4) (RGB: 127, 255, 212)
Electric Blue (Hex:7DF9FF) (RGB: 125, 249, 255)
Cyan (web color Aqua) (Electric Cyan) (Hex: #00FFFF) (RGB: 0, 255, 255)
Turquoise Blue (Hex: #00FFEF) (RGB: 0, 255, 239)
Bright Turquoise (Hex: #08E8DE) (RGB: 8, 232, 222)
Turquoise (web color) (Hex: #30D5C8) (RGB: 48, 213, 200)
Capri (web color: Deep Sky Blue) (Hex: #00BFFF) (RGB: 0, 191, 255)
Process Cyan (Pigment Cyan) (Printer's Cyan)(Deep Aqua) (Hex: #00B7EB) (RGB: 0, 180, 247)
Ukrainian Azure (color of Ukrainian Flag) (Hex: #42ADDE) (RGB: 66, 173, 222)
United Nations Blue (United Nations Azure) (Hex: #5B92E5) (RGB: 91, 146, 229)
Cornflower Blue (web color) (Hex: #6495ED) (RGB: 100, 149, 237)
Bright Cerulean (Crayola: Cerulean) (Hex: #02A4D3) (RGB: 2, 164, 211)
Bondi Blue (Crayola: Blue-Green) (Hex: #0095B6) (RGB: 0, 149, 182)
Rich Electric Blue (Hex: #0892D0) (RGB: 8, 146, 208)
Cerulean (Hex: #007BA7) (RGB: 0, 123, 167)
Steel Blue (web color) (Hex: #4682B4) (RGB: 70, 130, 180)
Air Force Blue (Hex: #5D8AA8) (RGB: 93, 138, 168)
Agate Blue (Hex: #44719B) (RGB: 68, 113, 155)
Medium Persian Blue (Hex: #0067A5) (RGB: 0, 103, 165)
Swedish Azure (color of Swedish flag) (Hex: #005B99) (RGB: 0, 91, 153)
Indigo Dye (Hex: #1A5798) (RGB: 17, 80, 147)
Bright Indigo (Crayola: Indigo) (Hex: #4F69C6) (RGB: 79, 105, 198)
Royal Blue (web color) (Hex: #4169E1) (RGB: 65, 105, 225)
Dodger Blue (web color) (Hex: #1E90FF) (RGB: 30, 144, 255)
Azure (Hex: #007FFF) (RGB: 0, 127, 255)
Deep Azure (Crayola: Blue) (Hex: #0066FF) (RGB: 0, 102, 255)
BLUE (Hex: #0000FF) (RGB: 0, 0, 255)
Cerulean Blue (Hex: #2A52BE) (RGB: 42, 82, 190)
Denim (Hex: #1560bd) (RGB: 21, 96, 189)
Medium Navy Blue (Crayola: Navy Blue) (Hex: #0066CC) (RGB: 0, 102, 204)
Sapphire (Maerz and Paul) (Hex: #0F52BA) (RGB: 15, 82, 186)
Medium Electric Blue (Hex: #035096) (RGB: 3, 80, 150)
Cobalt Blue (Hex: #0047AB) (RGB: 0, 71, 171)
Persian Blue (Hex: #1C39BB) (RGB: 28, 57, 187)
Azul (Hex: #002BB8) (RGB: 0, 43, 184)
Medium Blue (web color) (Hex: #0000CD) (RGB: 0, 0, 205)
Han Blue (Hex: #446CCF) (RGB: 68, 108, 207)
Electric Ultramarine (Hex: #3F00FF) (RGB: 63, 0, 255)
Westminster (Hex: #5F00FF) (RGB: 95, 0, 255)
Indigo (Electric Indigo) (Hex: #6600FF) (RGB: 102, 0, 255)
Medium Slate Blue (web color) (Hex: #7B68EE) (RGB: 123, 104, 238)
Deep Lavender (web color Medium Purple) (Hex: #9370DB) (RGB: 147, 112, 219)
Lavender (Hex: #B57EDC) (RGB: 181, 126, 220)
Lavender Indigo (Hex: #9457EB) (RGB: 148, 87, 235)
Deep Indigo (web color: Blue-Violet) (Hex: #8A2BE2) (RGB: 138, 43, 226)
Pigment Indigo (web color: Indigo) (Hex: #4B0082) (RGB: 75, 0, 130)
Persian Indigo (Regimental) (Hex: #32127A) (RGB: 50, 18, 122)
Dark Azure (Pantone Blue #286) (Hex: #0038A8) (RGB: 0, 56, 168)
International Klein Blue (Hex: #002FA7) (RGB: 0, 47, 167)
Dark Powder Blue (Smalt) (Hex: #003399) (RGB: 0, 51, 153)
Ultramarine (Hex: #120A8F) (RGB: 18, 10, 143)
Dark Blue (web color) (Hex: #00008B) (RGB: 0, 0, 139)
Navy blue (web color) (Hex: #000080) (RGB: 0, 0, 128)
St. Patrick's Blue (Hex: #23297A) (RGB: 35, 41, 122)
Dark Sapphire (Sapphire ( (Hex: #082567) (RGB: 8, 37, 103)
Midnight Blue (web color) (Hex: #191970) (RGB: 25, 25, 112)
Dark Midnight Blue (Crayola: Midnight Blue) (Hex: #003366) (RGB: 0, 51, 102)
Prussian Blue (Berlin Blue) (Hex: #003153) (RGB: 0, 49, 83)
Dark Indigo (Hex: #310062) (RGB: 49, 0, 98)
Dark Electric Blue (Hex: #536878) (RGB: 83, 104, 120)

Shades and variations

Blue is between violet and green in the spectrum of visible light

Blue is the colour of light between violet and green on the visible spectrum. Hues of blue include indigo and ultramarine, closer to violet; pure blue, without any mixture of other colours; Cyan, which is midway on the spectrum between blue and green, and the other blue-greens turquoise, teal, and aquamarine.

Blues also vary in shade or tint; darker shades of blue contain black or grey, while lighter tints contain white. Darker shades of blue include ultramarine, cobalt blue, navy blue, and Prussian blue; while lighter tints include sky blue, azure, and Egyptian blue. (For a more complete list see the List of colours).

Blue pigments were originally made from minerals such as lapis lazuli, cobalt and azurite, and blue dyes were made from plants; usually woad in Europe, and Indigofera tinctoria, or true indigo, in Asia and Africa. Today most blue pigments and dyes are made by a chemical process.

In science and industry

Pigments and dyes

Blue pigments were made from minerals, especially lapis lazuli and azurite (Cu3(CO3)2(OH)2). These minerals were crushed, ground into powder, and then mixed with a quick-drying binding agent, such as egg yolk (tempera painting); or with a slow-drying oil, such as linseed oil, for oil painting. To make blue stained glass, cobalt blue (cobalt(II) aluminate: CoAl2O4)pigment was mixed with the glass. Other common blue pigments made from minerals are ultramarine (Na8-10Al6Si6O24S2-4), cerulean blue (primarily cobalt (II) stanate: Co2SnO4), and Prussian blue (milori blue: primarily Fe7(CN)18).

Natural dyes to colour cloth and tapestries were made from plants. Woad and true indigo were used to produce indigo dye used to colour fabrics blue or indigo. Since the 18th century, natural blue dyes have largely been replaced by synthetic dyes.


sRGB rendering of the spectrum of visible light
Colour Frequency Wavelength
violet 668–789 THz 380–450 nm
blue 606–668 THz 450–495 nm
green 526–606 THz 495–570 nm
yellow 508–526 THz 570–590 nm
orange 484–508 THz 590–620 nm
red 400–484 THz 620–750 nm

Human eyes perceive blue when observing light which has a wavelength between 450–495 nanometres. Blues with a higher frequency and thus a shorter wavelength gradually look more violet, while those with a lower frequency and a longer wavelength gradually appear more green. Pure blue, in the middle, has a wavelength of 470 nanometres.

Isaac Newton included blue as one of the seven colours in his first description the visible spectrum, He chose seven colours because that was the number of notes in the musical scale, which he believed was related to the optical spectrum. He included indigo, the hue between blue and violet, as one of the separate colours, though today it is usually considered a hue of blue.

In painting and traditional colour theory, blue is one of the three primary colours of pigments (red, yellow, blue), which can be mixed to form a wide gamut of colours. Red and blue mixed together form violet, blue and yellow together form green. Mixing all three primary colours together produces a dark grey. From the Renaissance onwards, painters used this system to create their colours. (See RYB colour system.)

The RYB model was used for colour printing by Jacob Christoph Le Blon as early as 1725. Later, printers discovered that more accurate colours could be created by using combinations of magenta, cyan, yellow and black ink, put onto separate inked plates and then overlaid one at a time onto paper. This method could produce almost all the colours in the spectrum with reasonable accuracy.

In the 19th century the Scottish physicist James Clerk Maxwell found a new way of explaining colours, by the wavelength of their light. He showed that white light could be created by combining red, blue and green light, and that virtually all colours could be made by different combinations of these three colours. His idea, called additive colour or the RGB colour model, is used today to create colours on televisions and computer screens. The screen is covered by tiny pixels, each with three fluorescent elements for creating red, green and blue light. If the red, blue and green elements all glow at once, the pixel looks white. As the screen is scanned from behind with electrons, each pixel creates its own designated colour, composing a complete picture on the screen.

On the HSV colour wheel, the complement of blue is yellow; that is, a colour corresponding to an equal mixture of red and green light. On a colour wheel based on traditional colour theory (RYB) where blue was considered a primary colour, its complementary colour is considered to be orange (based on the Munsell colour wheel).

Scientific natural standards

  • Emission spectrum of Cu2+
  • Electronic spectrum of aqua-ions Cu(H2O)2+

Why the sky and sea appear blue

Of the colours in the visible spectrum of light, blue has a very short wavelength, while red has the longest wavelength. When sunlight passes through the atmosphere, the blue wavelengths are scattered more widely by the oxygen and nitrogen molecules, and more blue comes to our eyes. This effect is called Rayleigh scattering, after Lord Rayleigh, the British physicist who discovered it. It was confirmed by Albert Einstein in 1911.

Near sunrise and sunset, most of the light we see comes in nearly tangent to the Earth's surface, so that the light's path through the atmosphere is so long that much of the blue and even green light is scattered out, leaving the sun rays and the clouds it illuminates red. Therefore, when looking at the sunset and sunrise, the colour red is more perceptible than any of the other colours.

The sea is seen as blue for largely the same reason: the water absorbs the longer wavelengths of red and reflects and scatters the blue, which comes to the eye of the viewer. The colour of the sea is also affected by the colour of the sky, reflected by particles in the water; and by algae and plant life in the water, which can make it look green; or by sediment, which can make it look brown.

Atmospheric perspective

The farther away an object is, the more blue it often appears to the eye. For example, mountains in the distance often appear blue. This is the effect of atmospheric perspective; the farther an object is away from the viewer, the less contrast there is between the object and its background colour, which is usually blue. In a painting where different parts of the composition are blue, green and red, the blue will appear to be more distant, and the red closer to the viewer. The cooler a colour is, the more distant it seems.

Blue eyes

Blue eye Stephen
Blue eyes actually contain no blue pigment. The colour is caused by an effect called Rayleigh scattering, which also makes the sky appear blue.

Blue eyes do not actually contain any blue pigment. Eye colour is determined by two factors: the pigmentation of the eye's iris and the scattering of light by the turbid medium in the stroma of the iris. In humans, the pigmentation of the iris varies from light brown to black. The appearance of blue, green, and hazel eyes results from the Rayleigh scattering of light in the stroma, an optical effect similar to what accounts for the blueness of the sky. The irises of the eyes of people with blue eyes contain less dark melanin than those of people with brown eyes, which means that they absorb less short-wavelength blue light, which is instead reflected out to the viewer. Eye colour also varies depending on the lighting conditions, especially for lighter-coloured eyes.

Blue eyes are most common in Ireland, the Baltic Sea area and Northern Europe, and are also found in Eastern, Central, and Southern Europe. Blue eyes are also found in parts of Western Asia, most notably in Afghanistan, Syria, Iraq, and Iran. In Estonia, 99% of people have blue eyes. In Denmark 30 years ago, only 8% of the population had brown eyes, though through immigration, today that number is about 11%. In Germany, about 75% have blue eyes.

In the United States, as of 2006, one out of every six people, or 16.6% of the total population, and 22.3% of the white population, have blue eyes, compared with about half of Americans born in 1900, and a third of Americans born in 1950. Blue eyes are becoming less common among American children. In the US, boys are 3–5 per cent more likely to have blue eyes than girls.


Lasers emitting in the blue region of the spectrum became widely available to the public in 2010 with the release of inexpensive high-powered 445-447 nm laser diode technology. Previously the blue wavelengths were accessible only through DPSS which are comparatively expensive and inefficient, however these technologies are still widely used by the scientific community for applications including optogenetics, Raman spectroscopy, and particle image velocimetry, due to their superior beam quality. Blue gas lasers are also still commonly used for holography, DNA sequencing, optical pumping, and other scientific and medical applications.

In nature

Blue compounds are relatively rare in nature.


  • When an animal's coat is described as "blue", it usually refers to a shade of grey that takes on a bluish tint, a diluted variant of a pure black coat. This designation is used for a variety of animals, including dog coats, some rat coats, cat coats, some chicken breeds, some horse coat colours and rabbit coat colours. Some animals, such as giraffes and lizards, also have blue tongues.

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