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Friday, July 17, 2015

My Favourite Colour Doesn't Exist

Here's a fascinating presentation from the Royal Institution explaining how and why we perceive the colour purple (or more properly, magenta), even though it doesn't show up on the colour spectrum.  


Jeff Shyluk said...

Our ideas of colour theory vastly predate modern physics, something that the RI glosses over quickly. It would be much like trying to explain televangelism by using a only Gutenberg Bible.

Fact is, we don't have a proper working model of colour. No matter which one we use, there are still gaps in our understanding. The spectrum model endures because it is easy to teach. The colour wheel is inaccurate, but on the other hand it works well enough most of the time and remains useful.

Luminance-based models such as HSV are more accurate, but require three-dimensional shapes to explain colours. These are known as colour spaces. The Munsell system is a prototypical luminance system, and among other things it is able to precisely describe magenta.

RI also fails to mention the difference between additive and subtractive mixing - the instructor only uses additive, and poorly at that. Basically. additive uses light ("torches"), while subtractive uses pigment ("paints'). If you watch carefully, the cameraman must use a creative exposure level to reach additive white, since the instructor is using impure light sources (lightbulbs) and an inferior medium of reflection (paper) as well as broadcast (video).

If he were to do the same exercise using subtractive mixing, he would achieve brown. Anybody who has tried to mix paint and did not know anything about colour recipes will eventually achieve brown. Advanced colour recipes require a background in organic chemistry to achieve, although you can always follow someone else's recipe if you know how. So, making magenta is much more than simply mixing red and blue. For example, the royal purple I use in iconography uses 11 different hues mixed in proportion. My class just keeps a pot of it handy because it's a chore to mix small batches.

Apart from brushwork which can be learned given time, the Great Masters above all perfected their proprietary colour mixes, since they all produced their own pigments and paint formulations. That's why their works are so hard to reproduce, especially by some purple-shirt-wearing dude waving around flashlights. You can spend a lifetime trying to understand colour. When you do, you'll likely discover that you are better off exploiting that knowledge rather than explaining it. That's why the colour wheel has persevered for so long.

Earl J. Woods said...

Thanks for the insight, Jeff - always illuminating and colourful.