Why do we paint the ceilings of our front porches blue?
Colors with shorter wavelengths, including green and blue, usually have a calming effect, whereas colors with longer wavelengths, such as red, stimulate the nervous system. On pleasant days, the porch is where Southerners gather to relax and catch up with neighbors. Since the blue ceiling resembles the sky, it can promote the feeling of an extended day, which helps during the shorter days of winter.
In the South, particularly South Carolina and Georgia, porches, shutters and window and door frames were painted "haint blue" to keep out "haints," or evil spirits. It was believed that haints could not cross over water and painting these entrances to resemble water was a way to trick them. This folklore can be attributed to the Gullah, a group of African-Americans, originally from rice-growing regions of West Africa, who lived on the coasts of South Carolina and Georgia. Over the years, the concept spread throughout the South.
People also noticed the blue paint repelled insects, and some surmised it was because the insects were fooled into believing the blue ceiling was the sky, a place where they were in danger of being eaten. It's likely, however, that substances once used in paint actually repelled insects. The chemical composition of paints has since changed, but many blue porch ceilings are still around.