Why are most barns painted red?
The simple answer is because Red paint is cheap. The cheapest paint there is, in fact. But the reason why it’s so cheap is the interesting part.
Red Ochre-Fe2O3- is a simple compound of iron and oxygen that absorbs yellow, green and blue light and appears red. It’s what makes red paint red. It’s also really cheap because it’s really plentiful. And it’s plentiful because of nuclear fusion in dying stars.