Have you ever noticed that most barns are red? There's a scientific reason for that.
A few hundred years ago European farmers started painting their barns with a mixture of linseed oil, milk, and lime. Believe it or not, the combination made a pretty good paint that protected wood. Sometimes they'd also add ferrous oxide, also known as rust, to the mix.
Rust kills fungi and moss. When they grow on a barn they trap moisture in the wood, which leads to decay. Painting a barn with rusty paint was the best way to keep it strong and dry.
After a while, red barns became a tradition in Europe and over here in America. Once commercial paints became available, the tradition continued, since red paint was cheap.
White is the second most popular color for barns, since at some point whitewash became even cheaper than red paint. But today, you'll see barns in many different colors.