The explanation seems to be that this colour was cheap. The tradition seems to have been exported to the United States where it developed into more of an iconic image of rural life. To make the colour, richer folk mixed powdered ochre with linseed oil, turpentine and a liquid dessicant. Others simply mixed red ochre pigment with water. The resulting red colour is known as sang de boeuf in French ('ox blood') and some say that a few people mixed real ox blood with linseed oil.
The stables at the Chateau of Montpoupon.
Newly painted doors and shutters on a barn and garage in Preuilly.Source: Au temps de Chaumussay by Michel Brouard.