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Comment by kdmccormick | Hacker News Reader

Did they proofread this?

> The primary colours(yellow, red & blue) we were taught to paint with in school are wrong. The actual correct primary colours are yellow, magenta & cyan. The proof is in your printer cartridges.

...but two paragraphs later:

> Primary: red, yellow and blue, these colours can not be made from any other colours and are the building blocks of the other categories.

(My vague and possibly-incorrect understanding is that any three hues can be used as "primary hues", but different choices will result in different hue spaces, and it's just that CMY and RBY produce spaces that are useful in printing and painting, respectively.)

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Both of those statements are correct in context.

RGB if a thing is emitting light.

CMYK if a thing is reflecting light.

So it is true to say "Red, green, and blue are the basic building blocks of other colours"

It is also true to say "When you were told in primary school that the primary colours for your paints were red, green, and blue, this was untrue"

I do actually think that this is an example of a somewhat muddled thought process that is jumping from one thing to a other pretty eratically, or perhaps of something being edited such that it is now confusing to a reader going over it for the first time, honestly the whole thing reads a little like it was written by someone who really enjoys stimulants and can't keep their focus on one thing. But _technically_ I don't think any of the content is _wrong_ (obviously this means excluding ~70% of the content because it's largely about how people feel, and this is probably never _wrong_ but it's also not a matter of fact...)

No, actually, my bad, I went back and read that bit over again for a third time and it does actually say red yellow blue aren't primary, but that the primary colours are red yellow and blue.

You were correct and I jusy managed to misread the article twice....

> It is also true to say "When you were told in primary school that the primary colours for your paints were red, green, and blue, this was untrue"

The reason that red, green and blue are sometimes stated as primary colors in the context of mixing ink layers is that red and green and blue are rather vague terms. What is meant by red in this context would more exactly be called magenta and green is used to designate cyan. Wikipedia puts it this way[1]:

> Before the color names cyan and magenta were in common use, these primaries were often known as blue and red, respectively, and their exact color has changed over time with access to new pigments and technologies.

Also I think education about primary colors is just a mess and the same Wikipedia article[1] talks about this too:

> Elementary art education materials, dictionaries, and electronic search engines often define primary colors effectively as conceptual colors (generally magenta, yellow, and cyan; or red, green, and blue) that can be used to mix "all" other colors and often go further and suggest that these conceptual colors correspond to specific hues and precise wavelengths. Such sources do not present a coherent, consistent definition of primary colors since real primaries cannot be complete.

[1] https://en.wikipedia.org/wiki/Primary_color

According to Wikipedia RYB aka artist’s primaries work by accident:

“One reason the artist's primary colors work at all is due to the imperfect pigments being used have sloped absorption curves, and change color with concentration. A pigment which is pure red at high concentrations can behave more like magenta at low concentrations. This allows it to make purples that would otherwise be impossible. Likewise, a blue that is ultramarine at high concentrations appears cyan at low concentrations, allowing it to be used to mix green. Chromium red pigments can appear orange, and then yellow, as the concentration is reduced. It is even possible to mix very low concentrations of the blue mentioned and the chromium red to get a greenish color. This works much better with oil colors than it does with watercolors and dyes.

The old primaries depend on sloped absorption curves and pigment leakages to work, while newer scientifically derived ones depend solely on controlling the amount of absorption in certain parts of the spectrum.

Another reason the correct primary colors were not used by early artists is they were not available as durable pigments. Modern methods in chemistry were needed to produce them.”

A common problem when people with different backgrounds discuss primary colors is that they associate different notions with the term "primary color". There are at least four different concepts regarding "primary color":

1. a set of real colorants or colored lights that can be combined to produce a gamut of colors -> "real" primaries like RGB or CMYK

2. a set of imaginary colors that can be combined to produce the whole gamut of colors a human with normal vision can see -> color space primaries like XYZ or LMS

3. a set of colors that an observer perceives as pure -> psychological primaries or more precisely unique hues like those used in NCS or CIECAM02

4. the colors that are best examples of the (considered to be universal) basic color terms -> psychological primaries or more precisely focal colors (focal colors are a different concept than unique hues but empirically they seem to coincide with the unique hues, so the primaries from NCS or CIECAM02 are good examples here too.)

> (My vague and possibly-incorrect understanding is that any three hues can be used as "primary hues", but different choices will result in different hue spaces, and it's just that CMY and RBY produce spaces that are useful in printing and painting, respectively.)

If you are happy spanning any arbitrary gamut than any three hues will do. If your ambition is to cover the whole gamut of normal human vision no three real colors will do. You will either have to use more than three or allow imaginary colors. On the other hand there are infinitely many sets of primaries to span a certain gamut. Wikipedia expresses this probably much better than I can[2]:

> All sets of real and color-space primaries are arbitrary, in the sense that there is no one set of primaries that can be considered the canonical set. Primary pigments or light sources selected for a given application on the basis of subjective preferences as well as practical factors such as cost, stability, availability etc. Color-space primaries can be subjected to meaningful one-to-one transformations so that the transformed space is still complete and each color is specified with a unique sum.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1404500/

[2] https://en.wikipedia.org/wiki/Primary_color

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