Colour Theory

Colour White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow. We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is “split up” by raindrops.

The colours of the rainbow: Red Orange Yellow Green Blue Indigo Violet wavelength ROY G BIV

Additive Colour Theory White light can be split up to make separate colours. These colours can be added together again. The primary colours of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding red and green makes yellow Adding all three makes white again

Subtractive Colour Theory Deals with the reflected light Different pigments absorb different colours The primary colours of pigments are magenta, yellow and cyan. Adding yellow and cyan makes green Adding magenta and yellow makes red Adding all 3 makes black (all light absorbed) Adding magenta and cyan makes blue

Only red light is reflected Seeing colour The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: Homework White light Only red light is reflected

A white hat would reflect all seven colours: A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light A white hat would reflect all seven colours: White light

A black tuxedo would absorb all seven colours: A pair of yellow raincoat would reflect yellow light and absorb all others yellow light A black tuxedo would absorb all seven colours: No light reflected

Using coloured light If we look at a coloured object in coloured light we see something different. For example, consider a soccer uniform: Shirt looks red White light Shorts look blue

In different colours of light the clothes would look different: Red light Shirt looks red Shorts look black Shirt looks black Blue light Shorts look blue

Some further examples: Object Colour of light Colour object seems to be Red socks Red Blue Black Green Blue teddy Green camel Magenta book Homework

Using filters Red Filter Filters can be used to “block” out different colours of light: Red Filter Magenta Filter

Investigating filters Colour of filter Colours that could be “seen” Red Green Blue Cyan Magenta Yellow

Red Blue Green White Yellow Cyan Magenta