Professor (Dr) Surjit Singh Bhatti, Calgary (Canada)

Imagine how dull the world would appear if all objects around us had only one color. Our view of everything would become ‘monochromatic’. The hundreds of colors we see include black, white, gray, tans, and browns, which are called ‘Neutral colors’. It is the riot of colors that makes life lovely. There are three different sources of colors,  organic or synthetic dyes (pigments), the spectrum of light rays (electromagnetic waves) from the stars (mostly the sun), and hot flames. The inner surfaces of our eyes contain specialized cells (called photoreceptors) that are sensitive to light and relay messages to our brains. They are of two types: cones (sensitive to color) and rods (more sensitive to intensity). We are able to “see” an object when light from the object enters our eyes and strikes these photoreceptors.

The Wheel of Colors

‘The color wheel’ was invented in 1666 by Isaac Newton to help in the visualization of different pigment colors and their relationships with new colors. It shows three primary pigment colors and the manner in which they can be combined to create new (secondary and tertiary)) pigment colors. Each one of the primary and secondary colors on the color wheel has a distinct hue. The tone of a color is said to be altered when gray color is added to it. The addition of white color to any of these colors gives a distinct tint. The addition of black color gives them a different shade.

This wheel shows 12 colors: three primary colors, three secondary colors, and six tertiary colors. These are the colors that Artists and Painters use. They are obtained from either plant sources or from the synthesis of chemicals. These are the materials that let the light of certain colors pass through them and either absorb or reflect the light of other colors. Colors on the left side of this wheel (red, orange, yellow, red-purple, amber, vermilion) are called ‘Warm colors’ that appear closer to the observer than the ‘Cool colors’ on the right side (blue, green, blue-green, purple, violet, teal, white) that appear farther. Warm colors usually create energy and excitement, and evoke passion, while cool colors calm and relax.

Primary Colors of Pigments or dyes

Red, Blue, and Yellow are the three primary pigment colors to which our eyes are most sensitive. Humans possess trichromatic color vision or ‘trichromacy’. However, due to genetic factors, some humans and mammals have ‘dichromacy’, that is, they are sensitive to only two of the three colors. Dichromats are unable to distinguish between red and green or blue and yellow. No combination of other colors can produce the primary colors. Combining them gives us three secondary colors.

Secondary  Colors of Pigments or Dyes

   Tertiary  Colors  of Pigments or Dyes

Primary pigment colors mixed with their Secondaries give us six Tertiary colors. There can be many combinations of these colors, depending on how they are mixed.

Complementary Colors

Pairs of contrasting colors that exist directly across from one another on the Color Wheel are called ‘Complementary Colors’. Each pair has a warm color and a cold color. When combined, they cancel each other out and produce a grayscale or neutral color. The Color Wheel can be divided up any number of times to include several new colors between the basic hues. Red-Green is a typical example

 Colors of Light

Every wave of light has a particular wavelength that defines its color. Short waves have a higher frequency ( with higher energy) while long waves have a lower frequency (with lower energy). The wavelengths of waves in the visible light spectrum (VIBGYOR) increase from about 400 nanometers (nm) for Violet color to about 750 nm for Red color.  (1 nm = 10 ^{– 9} m). The harmful Ultra-Violet (UV) radiations (with wavelengths shorter than violet) and Infra-Red (IR) or heat radiations (with wavelengths longer than red) are not visible to us.

Primary colors of Light waves

Red, Green, and Blue are the three primary colors of light waves. Mixing them gives secondary colors of light, which are different from the secondary colors obtained by mixing primary colors of pigments or dyes. (White light is the presence while black is the absence of all colors.)

Secondary Colors of Light waves

There are two models ( called RGB and CMYK) that describe how secondary colors are produced.

RGB Color Model is based on the three primary colors; Red, Green, and Blue. It applies to screens of computers, televisions, and other electronic display devices. It is an ‘additive‘ model, in which the secondary colors; Cyan, Magenta, and Yellow colors of light are created by adding light waves of the primary colors in different proportions. It is the transmitted light that is used for the display. These can be combined with white light (or their intensities can be changed) to obtain different tints of colors or holograms.

CMYK  Color Model is based on Cyan (aqua), Magenta (pink), Yellow, and Key (black) colors. CMYK applies to painting and printing. It is a ‘subtractive‘ model, where colors are formed by the absorption of light. The wavelengths of light that are not absorbed,  then produce the color we see. When beams of light are mixed without any absorption, the colors are added. However, when we pass light through a colored filter, a subtractive process occurs. Some waves are absorbed (subtracted) and we only see the wavelengths that are given off.

  Colors in Nature

Rainbows arise due to unequal bending of the components of sun rays when they first undergo refraction, then dispersion, and finally a process called total internal reflection of light in water droplets. The spectrum is visible as an ‘arc’ of seven colors. Each wave of light produces a different color. Colors of stars, auroras, sunrise, and sunset are formed by the interplay of light (electromagnetic) waves in different ways.  Colors of shining metals, gemstones, and diamonds have similar origins.

Likewise, the colors of birds and butterflies can also be attributed to interactions of light waves with the pigments on their wings.  The colors of the eyes of all living creatures, including human beings, ranging from light blue or gray to dark brown, are determined by the amount of a pigment (called melanin), It is the colored part of the eye called the iris. This pigment consists of some proteins and also provides protection against the harmful  Ultra-Violet (UV) rays.

Origin of Colors of Light

When the atoms of a gas or vapor are excited by heating or by applying an electrical field, their (lightweight, negatively charged) particles called electrons (orbiting around a (positively charged, heavy) nucleus, are able to move from their normally stable  ‘ground’ state to ‘excited’ states with higher light energy levels. As they return to their ground state, they emit photons (or packets) of very specific light energy.  This energy corresponds to particular wavelengths of light, and so produces particular colors of light.

Each element has its own typical ‘Emission Spectrum‘. It is this characteristic spectrum of colors that enables its identification by Flame Tests. For example, copper produces a blue flame, lithium and strontium give red flames, calcium produces an orange flame, sodium produces a yellow flame, and barium emits a green flame.