Why is red the traditional color of barns?

In the late 1700's. farmers in North America began painting their barns with a homemade wood preservative to protect them from the weather. In the northern states where winter can be a tad bit more harsh, this preservative found to offer the best protection was made from lime, skim milk, and red iron oxide.

When this mixture dried, it gave the barn a durable, plastic-type finish. Because of the iron oxide, it gave the barn a bright red color. The use of this preservative became so widespread that by the early 1800's red had become the traditional color for barns.