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How come green is sometimes classified as a primary color if it is a mix of two colors?


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July 12, 2009 2:38PM

I would say that who ever is classifying green as a primary color doesn't know that it really is a secondary color! Correction of the above Green IS a primary colour, if one is considering light. In the art world, there are three primaries, red, yellow and blue, which, along with black and white, can produce all the other colours necessary for a painting a picture. For example, blue and red produce purple, blue and yellow make green, red and yellow make orange, black and white make grey, red and white make pink, all three 'primaries' make brown etc. As blue and yellow make green, in talking of art, green can be classified as a secondary colour because it is made up of two others. However, this is not true in physics when one is considering coloured light entering our eyes. In physics there are three primary colours, red, blue and green (NOT yellow!), as these are the three primary colours that make up the colour spectrum (rainbow) when white light is split into its constituent colours. We all learn in school that there are seven colours in the rainbow RED, orange, yellow, GREEN, BLUE, indigo and violet, but the orange and yellow colours are only formed as the red and green mix in different quantities. In actual fact, the colours mix as follows: red and blue produce magenta ( a pinky purple). Blue and green produce cyan (a pale turquoise) and red and green produce yellow (believe it or not!!). All three mixing together produce white light. This strange state of affairs can be proved in two ways. First, in most computer printers you will never find ink in the colours of the art primaries, but always the secondary colours magenta, cyan and yellow. Check this when you are replacing inks next time, or have a look on an Internet ink store catalogue to see the colours available. Secondly, if you have an old-style TV screen (the cathode ray type and not a liquid crystal or plasma type) then take a magnifying glass and have a really close look at the dots that make up the picture on the screen. You will find that any area that is white is made up of red, green and blue dots that look separate when viewed close up, but mix to form white when you step back a little. Also, yellow is similarly made of red and green mixing. It seems to defy logic but it's absolutely true. Another way to illustrate this is to cut out a disc of card and colour segments around the disc green intermingled with other segments coloured in red. If you poke a pencil through its centre and spin it like a top, you will find that the colours mix to form yellow rather than, say, brown. If you do the same with red, green and blue segments, the resultant colour will be white!