Why is a rose red?

This doesn’t really qualify as a mystery in this website because the science is well-understood. But, since I retired 20 years ago, I’ve been an artist. And although I would never feel confident about giving classes in art, I do enjoy explaining colour.

So… why does a red rose appear red? Normal sunlight, as we all know, comprises all the colours of the rainbow, plus more beyond which we can’t see but our skin certainly knows about it! The answer is that a red rose will absorb all colours except for red, which gets reflected back to our eyes.

A serious artist will tend to use pure pigments for their colours rather than colours pre-mixed in the factory. Each colour has a fascinating story which you can read about on the Winsor & Newton website. But even these pigments aren’t a pure blue or red, for example. Such colours don’t exist. Imagine mixing a pure red and a pure blue. In theory, the result will be black. The red will absorb all colours except for red, and the blue will absorb all colours (including red!) except for blue. But each pigment comprises a mixture of colours. For example, Cerulean Blue will contain a little green and Lemon Yellow also will contain a little green. Mix the two together and the result will be green, because that is the only colour common to both pigments. This is all explained very well in a famous book called Blue and Yellow Don’t Make Green.