Hundreds of years ago, farmers in Europe used linseed oil in combination with either lime or milk to produce a durable, tawny paint for barns. There are a couple of theories to explain the emergence of barns painted red. One idea is that farmers would add blood of a recently slaughtered animal to the oil, producing a burnt red color. Another theory is that farmers added rust to the oil mix as a way to kill off moss and mold. Europeans who moved to America brought with them the tradition of red barns. Red remained the most popular barn color until the cost of whitewash dropped and white barns began to appear.