Wikipedia:Reference desk/Archives/Science/2024 February 16

= February 16 =

Tertiary color
There are 3 primary colors and (3*2)/2 = 6/2 = 3 secondary colors. Then the number of tertiary colors should be (3*2*1)/6 = 6/6 = 1. Wikipedia's article List of colors by shade says that in theory this color should be black, but that in practice it is brown because blue pigments are so weak. Why is blue so weak?? Georgia guy (talk) 17:09, 16 February 2024 (UTC)


 * Color is such an interesting topic, because there are so many different ways to approach this complex subject!
 * If we take a very bland and scientific approach - like the one you might find in the main article about color mixing - you'll see a different (and more precise) way of describing the phenomenon. It also includes a link to a few useful citations.
 * We have to be careful to distill your question to its core, practical application, and to make sure we lay out some reservations: the observation is not universally true; but it manifests in some examples like mixing paints (especially the kind of paint you might buy in an art store).  I'm trying to avoid weasel-words, and also trying to avoid being unnecessarily technical here, but it's important that we're scientifically accurate!
 * If somebody - like an artist who mixes paint - describes "blue" as "weaker" (... in the context of how it qualitatively affects the outcome when mixing paints) - then they are probably dancing around the topic of opacity as it affects mixing pigments.
 * If this is what they mean, we can study scientific explanations for why the paint has this particular opacity. I'm reluctant to use a word like "weak" or "strong" here - we might disagree on which word is more apt - but it's helpful to know that most paints (like the ones you find in an art store) contain a chemical mixture of pigment in a binder (or sometimes a solvent).  The material is not "pure" pigment - it's a mixture.  The color of the mixture can be made more- or less- opaque by adjusting the concentration of the pigment.  Bafflingly, we might say that blue pigments are stronger, so paint companies can use less pigment in their paint to obtain a qualitatively equivalent amount of color, ... which makes for a bizarre reversal of qualitative language use..., which is confusing, and it's why we probably shouldn't use words like "weaker" or "stronger" when we're being scientific in our discussions about color.
 * All this aside, it would be misplaced if I attacked the fundamental premise here (as somebody who spends a lot of time scientifically studying color, and human perception of color, it's very tempting to shout ..."there's no such thing as a primary or secondary color...!" But ... human perception is involved here, so ... it's more complicated than that, too!)  Rather, I think what I would say is - "this simple model of color-primaries is useful only in very simplified cases, like kindergarten-level paint-mixing examples."  We do not have to work very hard to find examples where the simple model is insufficiently detailed to describe behaviors that are plainly visible to (most) everyone!  In fact, you found such an example!
 * Nimur (talk) 17:32, 16 February 2024 (UTC)
 * If you go back to that table you'll see that black is an absence of color. Mixing pigments removes color components. Additive colors are probably more what you want if you want to talk about a 'tertiary' color and that would be white or a pale color. NadVolum (talk) 23:01, 16 February 2024 (UTC)
 * A tertiary color is an intermediate color resulting from an even mixture of a primary and a secondary color, i.e. a mixture of the primaries in 3:1:0 proportion resulting in a less saturated form of the dominant primary color of the mixture. Philvoids (talk) 01:41, 17 February 2024 (UTC)
 * Note that this is given as a more recent "alternative definition" conflicting with the more traditional (and quite different) one of a mixture in a 1:2:1 proportion. --Lambiam 09:34, 17 February 2024 (UTC)
 * Using the RGB additive colour model, here are the three maximally light 1:2:1 mixtures:
 * and here are the six maximally light 3:1:0 mixtures:
 * Brown is more like a (not maximally light) 4:2:1 mixture: . --Lambiam 09:56, 17 February 2024 (UTC)
 * What about yellow? Zarnivop (talk) 10:34, 17 February 2024 (UTC)
 * As an even mixture of R and G, it is a secondary colour in the RGB model. --Lambiam 13:28, 17 February 2024 (UTC)
 * Yes, or a primary color in subtractive color systems or 575–585 nm spectral wavelength. Philvoids (talk) 13:50, 17 February 2024 (UTC)
 * As an even mixture of R and G, it is a secondary colour in the RGB model. --Lambiam 13:28, 17 February 2024 (UTC)
 * Yes, or a primary color in subtractive color systems or 575–585 nm spectral wavelength. Philvoids (talk) 13:50, 17 February 2024 (UTC)