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 that same on our version of the colour circle below seems rather a light blue!11 is in fact light blue, but looks more purple to us.
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 to warm on the right. Of course all colours should be gradient, nevertheless we choose frames 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 the Nord and South pole of the sphere, the exact middle being neutral grey. For practical reasons we did prefer to put everything on one surface, because a computer screen is still 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. In 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 of a print 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 (primer 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 of the screen.
Artist's paint can have very intensive colours not to be seen on an electronic screen, although it doesn't seem that way. If you mix colours on the screen it will give an expected and logical result. Yellow and blue will give green, yellow and red will give orange... 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' however 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) instead of 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 of the square is RGB yellow. The middle of the right side is the dark yellow colour 13 on our colour circle. The precise middle of the square is always the corresponding colour in the outer ring. The tone on the upper edge, one thirth length form the 'pure white', has made our inner circle.
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 RGB 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
Each brand of artist's paint present their colour cart on the internet. But we cannot see those colours on our screen, because it is always transformed in the three basic colours. The printed colour carts are not very good too, although some brands use up to seven basic colours for their prints. If you want to see the real colour, you have to look at the colour cart in the shop where the real paint has been added on strips of canvas.
All factories are free to chose the name for their colours, so you must realise that the used name of the colour can be misleading. An artist's paint which takes itself serious, as well as the artists using that paint, give the number of the used pigments. Some are pure and some are mixed. Those numbers can be checked on the site of pigment numbers, the colour index of artiscreation.com. You can click on any pigment to see it's composition or fabricage and ASTM lightfastness.
Which pigments are more reliable? Many years ago one could say the nonorganic pigments last for centuries to come, while the organical are more futile. So little organics where used by the best painters. Much saints on old fresco's now have olive green faces because the organic pink faded away while the underpaint of green clay did stay. However the Southamerican maya blue, made of indigo on palygorskite clay, remained as blue as 6000 years! And indigo was made of plants untill 1870. Carmine, coming from female insects called Coccus cacti, has also stayed quite good from gothic times until now, having become a bit brown. Alisarin crimson was a lake made from plants and did not maintain. Nowedays alisarin crimson is copied with a thirth branch of pigments, the petrochemical group. It is indicated as organic, but is in fact more 'organics made inorganic'. Their lightfastness is often I, the highest, but some of them are II or worse. Inorganics where originally digged pigments, later on augmented by chemically made colours, such as viridian, Prussian blue, later on cadmiums and cobalts. So it is not always an improvement when famous prigment factories have changed their cadmiums and cobalts into petrochemicals. They may still call it cadmium or cobalt, but if you check the pigment numbers it is revealed they are not.
Some examples. In Mussini oils cadmium yellow and red are still cadmium, the cobalt violets and blues are still cobalt. They stopped in selling cadmium green, which is a mixture of cadmium yellow with viridian (or phtalo green, the petrochemical). Their ceruleum blue or sky blue is still a cobalt-tin-oxide pigment, it was regarded as the most stable blue. Their Manga-Coelinblau, which was a cobalt too, is now a zinc oxide-phtalocyanin blue. Cobalt green is an irreplaceable pigment but not every brand still sell it.
Prussian blue is nowadays often a petrochemical replacement, as well als Naples yellow. Naples yellow was originally a lead pigment, lead antimonate. It is a commonly known that lead, cadmiums and cobalts are toxic pigments, but that means only you cannot eat them. I would't recommend them for body painting either. But for artists they should not be missed. Cobalts and cadmiums are always cat. I and they are very opaque and as basic layers they stand on the second place after digged minerals and leads. Petrochemicals can be cat. I, II or III, and are completely or partially transparant. Lead, cadmium and cobalt in small amount is completely natural while their petrochemical replacements are a pollution for the environnement.
Rublev produces a lot of oil paints with ancient pigments. (The synthetic iron oxides nevertheless have the same lightfastness as the digged.) Petrochemical pigments not only replace but also create new brilliant colours such as phtalogreen and phtaloblue, irreplaceable and with a lightfastness cat. I. Rublev also sells lead white, and they are right to do so, because it's beauty is not mached by titanium and zinc white, by the way two environnement polluters. Lead white is also much stronger for use as basic layers. Painted zinc white turns into a kind of glass during the years, jumping of the canvas in shatters.
Small view of the colour cart of Winsor&Newton water soluble oils. The number of colours is limited, but this oils make it possible not to need terpentine anymore. There are still cadmiums and cobalts present, but they are followed by a 'hue' colour, which simply means a petrochemical replacement. Cobalt green is missing.