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Physics

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  • $\begingroup$ Combinations of dyes will yield a subtractive color mix, since dye molecules absorb light of some wavelengths while passing others. If one has dye with particles which absorb everything but green, adding particles which absorb everything but red won't help any light get through. Paint, however, often has particles which reflect certain wavelengths while absorbing others. If one has paint with particles that only reflect green, adding particles that reflect red will allow some red light which would have been absorbed by a green particle... $\endgroup$
    – supercat
    Commented Feb 17, 2014 at 19:54
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    $\begingroup$ ...to get reflected by a red particle first. Since some light that reflects off a red particle will hit (and be absorbed by) a green particle before bouncing clear of the paint, the behavior of mixed paints isn't exactly additive, but it isn't subtractive either. Note that many paints include dyes, which do behave in subtractive fashion; two kinds of "blue" paints may appear identical, but yield very different results when combined with a "yellow" paint. Some kinds of yellow, mixed with true "blue" (not cyan) will yield green--not consistent with additive or subtractive color rules. $\endgroup$
    – supercat
    Commented Feb 17, 2014 at 19:58
  • $\begingroup$ And then there are metallic paints. There is a huge chasm between colour theory and actual colour work. Hopefully we've given @Hal the incentive to investigate further. $\endgroup$
    – hdhondt
    Commented Feb 18, 2014 at 9:36
  • $\begingroup$ Simplified color theory works nicely when when combining lights to achieve a certain look, or when combining dyes whose absorption spectra are largely non-overlapping, so as to achieve a certain look under some particular illuminating spectrum. The way materials' colors interact, though, depends upon their behavior at individual wavelengths. I wonder how hard it would be to construct a telescope-like device which would clearly show the spectral content of a spot at the center of the view field, marked with a cross-hairs or other indicator. That could assist understanding of "real" color. $\endgroup$
    – supercat
    Commented Feb 18, 2014 at 16:21
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    $\begingroup$ Look at the graph in my link. The outside "triangle" shows the colours the eye can see; the inner triangles show the range of colours various devices can produce. On those devices you will never see the colours outside the device's triangle, as they cannot be produced. $\endgroup$
    – hdhondt
    Commented Feb 10, 2022 at 4:39