Lecture 10: Colour Theory 1

• Spectral colour is a colour that is evoked by a single wavelength of light within a visible spectrum.
• A single wavelength, or narrow band of wavelengths generates monochromatic light.
• Every wavelength of light is perceived as a spectral colour in a continuous spectrum.
• The colours of similar or sufficiently close wavelengths are often indistinguishable by the human eye. 

Our perception of any colour is based on the eye receiving light that has been reflected from a surface or an object. 

The eye contains two kinds of receptors:

Rods convey shades of black, white and grey. Cones all the brain to perceive colour.

Types fo cones:

1. sensitive to the red-orange light

2. sensitive to green light

3. sensitive to blue-violet light

When a single cone is stimulated, the brain perceives the corresponding colour.

Because of this physiological response, the eye can be "fooled" into seeing the full range of visible colors through the proportionate adjustment of just three colours: RED, GREEN AND BLUE

• If our green cones are stimulated, we see "green".
• If our red-orange cones are stimulated, we see "red".
• If both our green and red-orange cones are simultaneously stimulated, our perception is “yellow”. 

Spectral colour

The eye cannot differentiate between spectral yellow, and some combination of red and green. The same effect accounts for our perception of cyan, magenta, and the other in-between spectral colours. 

Colour mode

Red, green and blue = relates to light

RGB - anything screen based

CMYK - anything printed

Chromatic values - hue, tone and saturation