First watch this ring. Which name would you give to the colours A, B, C and D? We would chose to A: warm green or ochre green, B dark gold ochre or light brown, C red brown and for D bluegreen, also called turquoise.
Physically this colours are however dark yellow (A), dark orange (B) and dark red (C). D is indeed bluegreen but on our version of the colour circle the colour seems rather a light blue!11 is light blue, but looks more purple.
Primary colours are 1, 3 en 5. We did prefer the version with the yellow on top because it shows the evolution from cold colours on the left tot warm on the right. Of course all colours should be gradient, nevertheless we choose a frame to give us a better insight in the colour spectrum. For a complete correct presentation a sphere should be used, the colours 1, 2 and 3 as well as everything in between could be a horizontal circle, with white and black as a Nord and South pole, the exact middle being neutral grey. For practical reasons we did prefer to put everything on one surface. A computer screen is nevertheless still in 2D. The outer ring shows the colours of the main ring mixed with grey.
Our brain does not experiences colours objectively. The tones of the primary colours in our circle are the most intense on the computer screen, called the RGB colours (also the green and the violet are called RGB colours). However the blue (5) looks rather dark to us. In paints it is named middle blue. Although the colour on the left between the middle blue (5) and vived green (6) is bluegreen, it resembles more light blue. The three basic colours construct all other colours and tones, include black and white . To light white is the sum of the the three primary colours, black the lacking of any light or colour. The three primary colours to light however are green, red and blue (with yellow being the mix of green and red. The printing of our colour circle is made with three basic colour pigments: yellow (1), violet (4) and blue (5). The pigment for the violet is called magenta, the printer creates vivid red with mixing magenta with yellow. Good printers have a colour more, the complete black. If one changes the mode from RGB to CMYK, the printer will additionally use that black pigment, because the RGB black is not that perfect. There is no white pigment in the printer, white will be limited to the colour of the used paper. Paints however have different pure whites, more intense then any colour of paper or gesso (on the canvas). Here on the screen there is no white in the center of our colour circle (25), it is in fact a light gray. If it would be really white, the light coming out of the screen would blind the eyes. Colour tones are somewhat different from one screen to another, it depends on the light source and the chosen clarity.
Artist's paint can have very intensive colours not to be seen on an electronic screen, although it doesn't seems that way. If you mix colours on the screen it will give an expected and logical result. Mixing pigments however will not always give a predictable result. For example mixing a vivid blue with a vivid red does not end in a vivid violet. For that purpose one should take a vivid violet pigment.
On our colour circle 13 looks what it is, dark yellow, thanks to the pure colours standing beside it. The A in the picture on top is however identical to the colour 13 on the second picture. On the first illustration is shown in B how we experience 14 as a brown, but it is identical to the dark orange on 14.
We do not have specific words in our vocabulary for the light tones of blue or green. On the contrary red with white we call pink, light violet is called lila. The name 'light red' indicates a red closer to orange on the colour circle, not the pink. The name 'dark yellow' on paint tubes is the most yellow kind of orange, not the ochre green shown in A or 13. The light blue (11) on our circle is not our choise, it is the mathematic mixture of the computer's most vivid blue with white. It does look a bit purple to us. Bluegreen is more recognisable in the ring of dark colours (between 17 and 18) then on the main ring.
Names as indigo, carmin, vermillion, purple and ultramarin are not colour names, but pigment names. Often used as if it where colour names nowedays, referring to an explicite tone. Indigo is a very dark tone of blue, vermillion is red going to orange, carmine to violet. Purple is the blue violet as produced by the purple snale and ultramarin is the blue of lapis lazuli, nowadays made synthetically.
For the construction of our colour circle we choose the tones as given by programs as Photoshop.
The indexed colour on the right top is RGB yellow. The middle of the right side is the dark yellow colour 13, the corresponding colour in the outer ring is always the precise middle of the square. The inner circle is the tone on the upper edge one thirth length form the 'pure white'.
A square is not the ideal represention (but very practical however) of colours, some pixels are repeated. The both corners on bottom for instance are the same 'total' black. The correct form of diagram would rather be a piece of pie, with the yellow on top of the circle radius. The program Painter uses a triangle which is a more logic representation.
Chosing colour in the program Corel Painter