The other colours come about by adding together responses to more than one colour. Your eyes respond only to red, green and blue. Different colours correspond to different frequencies of light. Rainbows are made up of light, which can have all the colours you're talking about.
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RAINBOW PRIMARY COLORS TV
The difference is that your eyes and a TV screen start with no light and you gradually build up to white, whereas your printer starts with white paper and so, as you add ink, you start subtracting colours from the white. Actually, these artistic colours are, from a physics perspective, the secondary colours of yellow, cyan (an artist’s blue) and magenta (an artist’s red). People often get confused by being told at school that the three primary colours are yellow, red and blue. Our computer and TV screens use the same primary colours as our eyes. If all three receptors are activated, we “see” white.
These are also used in colour printers, and the last one isn’t a rainbow colour. If two of these receptors are activated at the same time, we see three more colours: yellow (red + green), cyan (green + blue) and magenta (blue + red). These respond to red, green and blue light. We only have three colour receptors in our retinas. Also, violet appears reddish due to that encoding. Owing to the retinal encoding, the band we perceive as yellow is very narrow, whereas the red band is very broad. Similarly, orange is towards the yellowish part of the red band where green cones are still firing strongly. Hence the four basic colours of visual psychology are red, yellow, green and blue.Ĭyan looks distinct from blue because both green and blue cones are firing in that band, so it appears brighter. However, in the retina, colour information is encoded into red-versus-green and yellow-versus-blue channels for transmission to the optic cortex. The retina has cones with three opsin pigments that are sensitive to different colour bands, peaking in orangish-red, green and deep blue. Perhaps another culture would have come up with a different number of colours and a different mnemonic. In the UK, we are taught the mnemonic “Richard of York gave battle in vain”, so we look for the corresponding colours in the rainbow. While this was simply one of Newton’s mystical beliefs – others included alchemy and the philosopher’s stone, which could turn base metals into gold – it has become part of our cultural inheritance.
We have seven days of the week, seven natural notes in most Western music and, in Newton’s time, only seven planets had been discovered. It is said that Isaac Newton only perceived five colours in the rainbow and added two more (orange and indigo) because the number seven had mystical significance. Mike Follows Sutton Coldfield, West Midlands, UK I have never been able to see indigo and violet as separate colours. I am a volunteer at Woolsthorpe Manor, Newton’s family home, and have often demonstrated his prism experiment to visitors. He added orange and split purple into indigo and violet. This sort of mysticism fascinated Newton as much as science, so he thought there must be seven colours in the rainbow. However, the number seven had long been considered mystical, denoting perfection and completeness. This book was published in 1664, just before Newton started his experiments. For example, in his book Experiments and Considerations Touching Colours, Robert Boyle described the spectrum he produced with a prism as “denoting the five consecutions of colours Red, Yellow, Green, Blew, and Purple”. Prior to that, the spectrum had been thought to have five colours. In reality, there aren’t seven distinct bands, but multiple colours blending and shading into one another.Īround 1665, Isaac Newton performed experiments with a prism producing a spectrum in which he identified seven colours. Our perception of a rainbow is coloured (pun intended) by our expectation that there are seven colours.
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