Blue

Blue is a color that appears in many parts of the world around us. We can see it in a clear daytime sky, in deep water, and in many flowers, fruits, animals, and everyday objects. Unlike light, which can be described by measurable physical properties, color is also a result of how our eyes and brain respond to light. When light reaches an object, some wavelengths may be absorbed while others are reflected or scattered. The light that reaches our eyes is then processed by the visual system, allowing us to experience a particular color.

Blue light has relatively short wavelengths within the visible part of the electromagnetic spectrum, generally around 450 to 495 nanometres, although the exact limits of the color categories are not fixed. In daylight, the sky often looks blue because molecules in Earth's atmosphere scatter shorter wavelengths of sunlight more strongly than longer wavelengths. This process is called Rayleigh scattering. Blue can also look different depending on its surroundings and on the light that illuminates an object.

A blue surface may appear lighter in strong light and darker in shadow, while nearby colors can influence how we perceive it. Some objects look blue because they reflect more blue light toward our eyes than other visible wavelengths. For example, many blue pigments absorb a large part of the visible spectrum while reflecting blue light. In nature, blue can be produced in different ways: some materials contain pigments that absorb certain wavelengths, whereas some animals and plants create blue appearances through microscopic structures that scatter or reflect light.

Humans also use blue in many familiar contexts, such as maps, clothing, signs, artwork, and digital screens. On a screen, blue is one of the three primary light colors used in the RGB system, alongside red and green. By combining these three kinds of light at different intensities, screens can produce a wide range of colors.