Myths and conjecture surround the reason that the White House was painted white. Was it an arbitrary decision of the architect or the best color to preserve the building materials? No one knows for certain.

The exterior walls are made of limestone, quarried from the local Aquia Creek Quarry in Stafford, Virginia. In 1798 the walls were painted to protect the sandstone from damage caused by water and freezing winters. One could assume that the color white was chosen by the architect, Hoban. He may have just liked white, or the home it was based on was painted white.
There is a Washington myth which claims that people started calling it the White House after the British burned it in 1814. This was during the War of 1812. It had to be painted to conceal the scorch marks.
However, there had been many references to it as the White House long before that, and it was originally painted white before this burning occurred. Perhaps at that time, white paint was the best kind of paint to preserve the limestone.
In December of 1790, George Washington signed an Act of Congress setting aside land for the federal government. It was not to exceed ten square miles and was to be on the Potomac River.
President Washington and city planner Pierre L’Enfant picked the site which is now 1600 Pennsylvania Avenue. A competition was held to find an architect for the President’s House. Among nine contestants, Irish-American architect James Hoban won. Hoban based his neoclassical design on a project in The Book of Architecture by James Gibbs.
Construction began in 1792 and its first residents were John and Abigail Adams. They moved into the house in 1800, when it was almost completed. It was constructed by both paid and slave laborers, along with some stonemasons brought over from Scotland.
There have been several additions to the White House, and some remodeling over the years. In 1826, Hoban added the South Portico and in 1902 the Gallery and Executive Office Wing were added.
Harry S. Truman had the interior gutted and remodeled, except for the third floor between 1948 and 1952. It survived a second fire, which happened in the West Wing in 1929. The original exterior walls, however, are still the ones erected over 200 years ago.
Although we don't know a lot about why the paint color for the White House was chosen, we do know a lot about the house and the people who have lived in it over the years. For example:
So, although we know a lot, the reason the White House was painted white may never be known. Perhaps white was chosen because it is a clean, bright and new looking color. It’s a good color to portray a new country, a new government, and its people.