Blue is a popular and commonly occurring color in nature. Many things in our everyday lives appear blue or have hints of blue in them. In this article, we will explore some of the most common things that look blue and discuss why they appear this color.
Some quick answers to what looks blue include the sky, water, certain flowers, gemstones, fabrics, paints, and more. The reason these things look blue has to do with the physics of light and how different wavelengths are absorbed and reflected.
The Sky
One of the most ubiquitous things that appears blue is the sky. On a clear day, the sky has a rich, deep blue hue. This blue color is caused by how sunlight interacts with the gases in the atmosphere. As white sunlight enters the atmosphere, shorter wavelength blue light is scattered more than longer wavelengths. The scattered blue light is what gives the sky its characteristic color.
The main gases responsible for scattering blue light are nitrogen and oxygen. These molecular gases account for over 99% of the dry atmosphere. The nitrogen and oxygen molecules are much smaller than the wavelength of visible light. This causes the shorter blue wavelengths to be scattered more than orange, red, and yellow light.
Besides scattering, the sky can also look blue due to optical effects. Tiny particles in the atmosphere, like dust, smoke, or pollution can also scatter blue light. The scattering of sunlight by these particles produces the effect that makes distant mountains or the horizon look blue.
Water
Liquid water is another very common substance that appears blue. Whether it’s the ocean, a lake, a swimming pool, or even a glass of water, clear water has an unmistakable blue color.
The water molecules themselves don’t have any blue color. Water absorbs light in the red end of the visible spectrum and reflects light in the blue end. This selective absorption and reflection of different wavelengths gives large bodies of water their deep blue appearance.
Impurities dissolved in water can also intensify its blue color. For example, small amounts of copper ions can give a rich blue-green tint to water. This is the reason sometimes water in fountains or pools has a more vibrant blue-green color.
The Human Eye
Surprisingly, the human eye itself also looks blue when viewed from certain angles in good lighting. The distinctive blue color comes from the same physics of light scattering that makes the sky blue.
The surface of the eye, including the cornea and sclera, reflects back blue light more than other wavelengths. This is because the collagen fibers making up these structures are smaller than the wavelengths of light. With the right viewing angle, the eye’s surface reflects enough blue light to take on a blue tonal quality.
Blue Flowers
Many species of flowers across a wide range of plant families produce blue blossoms. Some examples of blue flowers include forget-me-nots, bluebells, cornflowers, iris, hydrangea, morning glory, delphinium, and plumbago.
The blue pigmentation in these flowers comes from anthocyanin pigments. Anthocyanins are water-soluble plant compounds that reflect blue and purple light. Different anthocyanin pigments result in different shades of blue.
Flowers may also appear blue due to structural color from light scattering or iridescence from multilayer petal surfaces. This structural blue color is seen in some orchids and Hoya flowers.
Blue Gemstones
There are a variety of gemstones that exhibit blue coloration. Some of the most popular blue gems include sapphire, lapis lazuli, turquoise, tanzanite, aquamarine, topaz, and kyanite. These all contain minerals that selectively absorb or reflect certain wavelengths to produce blue hues.
Sapphire gets its signature blue from the presence of trace amounts of iron and titanium. These transition metals produce vivid blue and purple colors through intervalence charge transfer.
Lapis lazuli contains lazurite, a feldspathoid silicate mineral that absorbs red and yellow light. This leaves the gemstone with an intense blue color.
Blue Fabrics
Many types of fabrics are dyed or treated to appear blue. Denim is the classic blue textile. The indigo dye used to color denim absorbs nearly every color except blue. This deep blue tone of denim comes from the indigo plant.
Other blue fabrics include blue chambray, velvet, linen, satin, and cotton. These textiles are colored with a range of blue dyes. Synthetic indigo and phthalocyanine dyes are common for achieving blue shades on fabric.
Blue Paints
Paint is one of the most flexible ways to make objects appear blue. Many formulations of oil and water-based paints come in various blue hues. Common blue pigments used in paints include ultramarine, cobalt blue, Prussian blue, phthalo blue, and indigo.
Ultramarine has been used by artists for centuries and originally came from the mineral lapis lazuli. Cobalt blue offers excellent intensity and lightfastness. Phthalo blue is a synthetic pigment known for its brightness. Each blue paint pigment has unique properties for creating different shades.
Blue Animals
While not extremely common, some animals display blue coloration. This is caused by blue structural coloration, pigments, or bioluminescence.
Some examples of blue animals include blue jays, blue tang fish, blue-ringed octopuses, blue morpho butterflies, blue crabs, blue frogs, and mandrills. Even rarer “blue” animals include lobsters, snakes, tarantulas, scorpions, and lizards.
Unique evolutionary adaptations produce blue color in each animal group. Butterfly wing scales reflect blue light. Octopus skin contains pigments that absorb other wavelengths. And some reptiles have anatomical structures that scatter blue.
Blue Foods
There are also some foods that can appear blue or turn foods blue:
| Blue Food | Source of Blue Color |
|---|---|
| Blueberries | Anthocyanin pigments |
| Blue raspberry flavoring | FD&C Blue No. 1 dye |
| Blue corn | Anthocyanin pigments |
| Blue cheese | Penicillium mold |
| Blue velvet cake | Blue food dye |
| Blue milk or ice cream | Anthocyanin powder |
Natural blue foods get their color from anthocyanin pigments. Artificial blue foods are dyed with colorants like FD&C Blue No. 1. Adding blue coloring can make many foods appear blue for aesthetic reasons.
Blue Man-Made Objects
Many consumer products and man-made objects also utilize the color blue:
– Blue jeans – Dyed with indigo
– Blue pens or pencils – Dyes like phthalocyanine blue
– Cars or bikes painted blue – Automotive paint containing phthalo blue pigments
– Blue bottles or containers – Colored glass or plastic
– Blue M&Ms – Dyes and food colorants
– Blue Play-Doh – FD&C Blue No. 1 dye
– Blue children’s toys – Paints or plastic
Companies use blue for marketing reasons and to associate their brand with qualities like tranquility, confidence, and intelligence. Blue is a popular color choice for consumer products.
Conclusion
In summary, many diverse objects in the natural world and man-made environment exhibit blue coloration. The sources of these blue hues include light scattering, plant pigments, minerals, dyes, structural color, and additives. Blue is a pervasive color caused by physical and chemical properties of materials that selectively reflect or transmit blue wavelengths of light. So when you observe something blue, it’s thanks to the fascinating interplay between light, matter, and perception.
