There are many older homes in the United States that have ceilings (especially of porches and decks) or shutters painted blue. The color is referred to as "haint" blue. The etymology of the word is unclear - it's not listed in the OED or in my Random House. Various websites say its of European derivation, but I suspect it's simply a corruption of the more familiar word "haunt," referring to ghosts.
"...the first painted strokes of Haint Blue adorned not the homes of the rich, but the simple shacks of African slaves. Known as the Gullah or Geechee people, the original Haint Blue creators were descendants of African slaves who worked on rice plantations in South Carolina and Georgia... They kept alive the traditions, stories, and beliefs of their ancestors, including a fear of haints."
Folklore says that some ghosts cannot cross water, so the color blue was apparently employed in order to confer upon a home some protection from evil spirits.
The actual shade of "Haint Blue" varies, as the formulas were mixed by hand with local pigments. Haint Blue can range from a pastel violet-blue, such as a periwinkle, to a rich shade of warm turquoise, and everything in between.Photo credits top, middle, and bottom.