When we were young, we were all taught that red, blue and yellow were the primary colours. The reason why they were the primary colours was that you can make other colours from those colours and you cannot make red, blue and yellow. The truth is that you are only one-third correct if you think red, blue and yellow are the only primary colours you see.
The primary colours really depend on the medium of use of the colours – digital, print or art. The definition of primary colours would be that they are pure hues that cannot be made from any other source of colour. We see colours with colour receptors cells, cones that detect red, green and blue wavelengths. All the colours that we know of are perceived by the wavelengths these colours give within the visible spectrum aka the human colour space.
In digital the primary colours are red, green and blue because when combined these colours make white and other colours when blended together. On a computer screen, you can make different colours like cyan, yellow and magenta when combining red, green blue by overlapping the colours. Red and blue create magenta; Blue and Green create cyan; Green and Red create yellow. RGB is also known as additive primaries because all colours combined create white. White is seen as a measurement of light. Using RGB is really how humans see colours with light waves reflecting into our eyes at different lengths creating different colours. Screens, scanner and monitors replicate this to create colours using different frequencies of energy.
In print, the primary colours are cyan, magenta and yellow because when combining these colours can make other colours together. In print dyes, inks and toners are used to create colours. Cyan, magenta and yellow are the only colours that cannot be created from any other source. These colours in print were originally derived from the earth. They are from plants and minerals extracted. These are process colours that are used on lithographic print and production printing because they create sharp renditions of colours to reproduce an image in a print. These are transparent colours because light transmits through the inks to reflect off the surface below. Black is added to CYM has a keytone colour to create better colours on paper. These are subtractive primary colours because the colour is experienced through the reflective light that was absorbed by the paper. There are two sets of subtractive primary colours we know of printer’s primaries (CMY) and artist’s primaries (RYB).
We learned the primary colours are red, yellow and blue because they were the primary colours of the artist to create colourful artwork. This is the easiest and quickest way to comprehend the use of colours as a beginner. By understanding how to use colours in your own drawings it is easier to comprehend what other artists did before. Red, yellow and blue is used when you are painting a portrait. Paints and markers can create black when all colours are combined and create other colours. But black is not needed to create any colour because red, blue and yellow are opaque. No extra colours are nesscessary. By looking at a painting and looking for the colour combination of certain colours the primary colours for painting and everyday use are red, blue and yellow. This trio is the basis of a lot of colour theory that exists.