Colour is the visual perception of different wavelengths of light such as red, green etc. Colour derives from the spectrum of visible light which interact with the colour sensitive cells of the retina to give the colour vision. Colour may be defined or quantified based on the degree by which the various colour sensitive cells are stimulated. The science of colour is the Chromatics that includes the perception of colour, origin of colour in the materials and involvement of brain. Colourology is the science of colours and their impact on human beings.

Some Light physics
Light is a part of Electromagnetic radiation which is characterized by wavelength and intensity. Only a small portion of light is detectable by the human eye. This part is known as visible spectrum which includes wavelengths ranging from 390 nm and 750 nm. Below this range is invisible Ultraviolet and above invisible Infrared. Visible light is a mixture (Polychromatic) of seven colours popularly known as VIBGYOR. Each colour (Monochromatic) has a particular wavelength. Of the seven colours, human spectral response is peak in the Green- Yellow region (550nm) because these colours are most abundant in nature. Yellow colour has more visibility than others so that is used in Sign boards, traffic signals etc. Even though only four colour sensitive cones are present in the human, eye different colours can be perceived through spectral combination of colours.

Colour objects

The colour of an object depends on the factors like, the physical nature of the object, environment in which it is placed and the perception by eye and brain. The object colour is perceived through the wavelength of light leaves from its surface. This depends on the incident light, reflective nature of surface, angle of illumination and viewing. The colour of the object depends on the reflecting light as well as the ability of constant perception irrespective of light intensity and viewing. This ability is known as Colour constancy. The opaque objects do not reflect light due to the characteristic nature of its surface. If the object scatters all wavelengths, it appears as white and if it absorbs all wavelengths, it becomes black. Some objects transmits light and may be Translucent which scatter the transmitting light and Transparent which do not scatter the transmitted light. If the object absorbs light or reflect, it appears in tinted determined by the wavelength of light. This property is known as Reflectance.

Colour temperature

It is the characteristic feature of visible light and is defined as the temperature of an ideal black body radiator that radiates light of comparable hue to that of light source. The Black body is an ideal physical body that absorbs all incident electromagnetic radiation. Colour temperature has great importance in Lighting, Photography, Astrophysics, TV, Video devices etc.  and is measured in terms of Kelvin having the symbol K. Colour temperature above 5000 K is cool colours with bluish white hue and lower colour temperatures between 2700 – 3000K are warm colours with yellowish white through red hue. Colour temperature is the surface temperature of the black body measured in Kelvin unit or Micro Reciprocal Kelvin Unit (mired).The colour temperature of light is not the actual temperature of the surface. For instance, the colour temperature of the incandescent bulb is its filament’s temperature. Most of the light sources do not follow the black body concept. In these cases, the colour temperature is the Correlated Colour Temperature (CCT) which is the colour temperature of the black body radiator to which the human colour perception matches.

Colour temperature is an important factor in TV and Digital camera etc. Higher grade Televisions have colour temperature set at 6500K through programmed settings. Many of the Digital cameras and Video Cams can adjust colour temperature by zooming into white background and setting manually the White balance. The device can then automatically adjust all other colours by taking the white as true white colour. White balancing is very important when the camera is using under Fluorescent lighting or changing the light from one source to another. Some cameras have automatic white balance settings to adjust the colour temperature.

Colour Vision in Man

Human eye can detect different colours due to presence of colour sensitive photoreceptors called Cones in the retina. Cones are also responsible for Bright vision( in day light) and Central vision. Cones contain the visual violet called Iodopsin similar to the Rhodopsin (visual Purple) of Rods. Human being is Trichromatic (detect three colours simultaneously) and has three types of cones in the retina. The cones belong to three categories.

  1. Short wavelength cones – S Cones or Blue cones

These cones are more sensitive to violet colour around 420 nm

  1. Long wavelength cones – L cones or Red cones

These are more sensitive towards 564 nm in the greenish yellow.

  1. Middle wavelength cones – M cones or Green cones

These are more sensitive in 534 nm

Each cone yields three signals based on the degree of stimulation called Tristimulus value. This Tristimulus value determines the Colour Space of human retina and it is estimated that human beings can distinguish around 10 million colour combinations. When the light is too strong, cones will be stimulated properly and Rods remain dormant. But if the light intensity is too low, cones remain unstimulated and a colurless response develops from the rods. Rods are less sensitive to light in the red range. In certain conditions of intermediate illumination, both rods and cones response and a change in colour perception occur. When the rods and cones are exposed to strong light, the photoreceptors remain de sensitized for a short time and the signal continues for a few seconds. The colour appearance during this period is faint due to lack of colour component. This phenomenon is known as Afterimage in which the eye can see the bright image for few seconds after looking away from it. The colour of the image will be a complementary colour.

Human beings can detect only three colours like Red, Green and Blue. These colours are called as Additive Primary colours. But the brain can detect other colours also by the mixing these colour signals in the brain.

Types of colours

Red, green and blue are the Primary colours of white light. The combination of all three of these colours will result in white. There are two types of Primary colours.

1. Additive colours

Additive colours are colours that are associated with emitted light directly from a source before an object reflects the light. These colours are red, green and blue. These are the colours we are probably most familiar with in association with television, and computer displays. The additive primary colours are red, green and blue. Secondary additive colours are produced by mixing two other additive primary colours together.

When these additive colours are mixed, they produce three other secondary colours. These are: Cyan, Magenta and Yellow. If all three of the additive colours were combined together in the form of light, they would produce white. Some examples where additive primary colours are used are, television, theatrical lighting, computer monitors etc.

2. Subtractive 

Subtractive colours are colours that are associated with reflected light. In this case the subtractive colours are blue red and yellow. These colours are associated with the subtraction of light and used in pigments for making paints, inks, coloured fabrics, and general coloured coatings that we see and use every day.

Complementary colours

When placed next to each other, complementary colors tend to look balanced.

  1. Violet and Yellow
  2. Indigo and orange
  3. Blue and Red
  4. Green and Magenta
  5. Yellow and Violet
  6. Orangeand Indigo
  7. Red and Blue
  8. Magenta and Green

Magenta is the eighth color and is not part of the visible spectrum, but is a combination of red and violet, thus combining the energies of those two colors. That is to say, that magenta helps us to use our earthly experience and grounding together with intense spiritual awareness. It can help to release past conditioning and help us to move forward.

Secondary subtractive colours are produced by mixing two other subtractive primary colours together. When these subtractive colours are mixed, they produce three other secondary colours. These are: Violet/purple,Orange, and Green.

Magnetic or Electric colours

In Colour Therapy, Red,Orange, and Yellow are referred to as magnetic/warm colours – Blue, Indigo and Violet are referred to as electric/cool colours. Generally speaking, the three higher colours are calming, and the three lower colours are stimulating and green is the balance between the two types of energy.

Colour in Psychology

Is our character is related to colour?

Everyone like colours. Our colour interest is related to our psychological and personality traits. These are the possible characters related to colour interest.


Red colour stands for passion, warmth, vigor, excitement, strength, vitality etc. When we see red colour, our pituitary stimulates leading to the secretion of Adrenaline from adrenal gland. The adrenaline causes, rise in BP, blood flow, appetite, increase in smell perception etc.

Persons choice red colour are outgoing in nature, have sudden mood swings, have compassion, have a positive approach, assertive in nature, have strong sex drive and more emotional. Light Pink colour express maternal affection.


Persons lovingOrangeare pleasant and cheerful and make good friends. They can be influenced by the opinion of others. They are usually sincere and generous in nature.

Orange colour increases ambition and motivates the creativity. But if a person is exposed to strong orange colour for long time, he may become restless. Orange colour increases appetite and induce sleep. When combined with blue colour, orange induces a feeling of stillness.


People love green colour are obedient and duty conscious, honest, straightforward, have normal sex drive, and attached to family relations. Green colour stimulates histamine production which causes dilation of blood vessels. It helps to reduce allergic reactions, gastrointestinal problems, improves eye sight (Surgeons use green colour in the room to increase sight).


Those who love blue ate thoughtful and meditative. In a stressful situation, they hold their belief and prefer to avoid the situation. They have control over their passion and consider the needs of fellow beings. Blue represents truth and harmony since it is the colour of heaven. Blue represents calm, stimulates protective instinct and prevents tanning. If combines with green, blue can cause an outburst of ingenuity. But too much blue colour can cause mood depressing.


People loving Purple colour are Intelligent and sharp and always sees the things which are overlooked by many person. They get enraged by slightest provocation and try to express their grief. They always exhibit creativity.

Purple is the colour of wealth and richness. Purple colour vibrates very fast in the spectrum and disappears quickly. Purple colour boosts the metabolic activities and has a healing effect. Purple colour stimulates the right part of the Bain and evokes imagination and thought. Since Purple is the colour of peace, it helps to cope up with fear and stress.


Yellow colour has great influence on the personality. Yellow lovers have vibrant imagination and energy. They are well organized and show clear vision and thinking. They are shy and always seek the help of friends and like to be loved

Yellow offers cheerfulness, wisdom and joy. Golden yellow colour stimulates spiritual attitudes and influence for peace. Yellow colour stimulates the nervous system and if children are exposed to too much yellow colour often become angry and cry. Yellow can also stimulates allergic response in some persons.


People love brown colour are meticulous in life activities and stick on their belief. They are reliable persons and will not take hasty decisions.

Brown is the colour of earth and strongly related to Sex drives and Fertility. It is the colour of environment and gives a sense of security. It positively helps the body and mind in doing jobs. Brown colour helps to reduce fatigue and mental depression by promoting neurotransmitters. Brown colour release neurotransmitters that induce sleep and prevent head aches.

Colour in Home                                

Colours used in rooms and other areas of the house have great importance in the feelings of inhabitance. Colour has psychological effects and provides a specific feeling for a space. We all have a colour choice but it is good to understand the effect of colours on human mind.


It is colour that calm body and mind and enhances dignity, awareness etc. Ideal places for Violet are Worship places, Hospitals, Bed room etc.


Indigo is the sedative colour of divine knowledge and mind. Indigo is applicable in bed rooms, entertainment room , study room etc.


It is the colour of calm, relaxation and healing. Blue is considered as the colour of communication. It can be used in any room except the rooms used for physical activities.


Green is the colour of understanding. It creates balance and harmony in the home and encourages tolerance. Green colour can be used in all rooms with varying shades. If other colours are used with green, the colour should match with green to keep the balance.


Yellow colour stands for confidence. It stimulates mental activities and creates a feeling of confidence. Yellow colour keeps to stay alert and very good to promote study. Yellow can be used in living rooms, study rooms etc. Yellow colour is bad for bed room since it keep the mind alert which will disturb the sleep.


Orange energizes your body and keep it warm. It stands for fun and encourage social living. Orange colour stimulates the mind for creativity. It is well suited for rooms in which creative activities are going on. It is not suitable for bed room and areas of possible stress, since these areas require clam and peace.


Red excites emotions and energizes the body. It also has a stimulatory effect on the digestive system. It stimulates the secretion of digestive enzymes and induces appetite. Red colour is suitable for any room especially dining room and kitchen. But red colour should be used carefully since the colour can make the space look smaller which can be oppressive. So various tones and depth of red can be used as per choice without creating the oppressive effect.


It is the eighth colour which is the combination of Red and Violet. Magenta is the colour of fulfillment and completeness. It stimulates thoughts and spiritual thinking. Magenta is ideal for class rooms, spiritual rooms, prayer rooms etc.


It is the cool colour that makes you calm. It stimulates the nervous system considerably and boost the immune system. Turquoise can be used in all rooms except in activity rooms.


Is the colour of love and passion. It encourages unconditional love. It stimulates the brain, soothes the body. Pink colour express maternity and is very good for children’s bed room. If you see Pink for some time, your anger will disappear.


White contains all colours and is the sign of purity and clarity. It energizes the thoughts and enhances the mind. White can be used in all rooms with other colours to enhance the beauty.

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