system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are the colours blue and purple relatively rare in nature?
gpt
When you look at things, their coloration comes from the light they reflect while absorbing the rest. A blue object absorbs all colors while reflecting only blue light.

Blue light is the part of the visible spectrum with the most energy. Since plants want to absorb as much energy as possible, they didn't evolve to reflect blue light.

Pretty much the only time plants use blue pigments is when they want to attract attention. Blue flowers, blue fruits etc.

Many animals get their pigments from the food they eat. Herbivores eat the plants, predators eat the herbivores. Flamingos are pink due to the red shrimp they eat. The shrimp are red due to the plants they eat.

So on the one hand, blue doesn't make for good camouflage because plants don't want to be blue. And on the other hand, animals can't consume plants for their blue pigments either.

Most animals that do appear blue aren't blue because of pigments (which the usual way organisms display color). Instead, they evolve textured surfaces that bend light and reflect it in a different wavelength to appear blue.

As you can imagine, that's a really unusual adaptation so there's not that many animals that have it.