[HerbManic]

This reminding me of something my granddad demonstrated once.

He used to work on yachts a fair bit and over the years he noticed the fading patterns for different colour paints.

Yellow paint would fade, red paint would fade. But if you mixed them 50/50 into orange, it wouldn't fade. That's why they had so many orange boats in the bay. Figure that one out.

[Citizen_Lame]

It comes down to each pigment acting as a UV shield for the other. Paint fades because specific wavelengths of light (mostly UV and high-energy visible light) break down the chemical bonds in pigment molecules. The key is that different pigments are vulnerable to different wavelengths.

Yellow pigment absorbs blue and violet light. That's what makes it look yellow, it reflects the longer wavelengths and soaks up the shorter ones. But the UV and violet radiation it's absorbing is also what gradually destroys it.

Red pigment does something similar but across a different band, it absorbs greens and shorter wavelengths, and that absorption is what degrades it over time.

When you mix them 50/50 into orange, each pigment is absorbing the wavelengths that would have destroyed the other one.