[anigbrowl]

That seems too pat an explanation; I've sen a lot of very nice red rooms, and in other cultures it has more positive associations than in the Anglosphere. Also, how you react to color depends on the saturation as well as the hue.

In any case, this doesn't answer the question of why more people don't (or historically didn't) paint the outside of their houses red.

[randomdata]

Perhaps because houses are often made of materials that are not wood? Stone and brick homes are almost never painted, thus setting a theme for homes that deviates from red. Houses are also rather small in comparison to barns. It could just be a matter of being able to afford other options at the smaller scale.