Why is the White House white? via Quora
Answer by Zachary Conley
Here is the official answer to this exact question given by The White House Historical Association:
The building was first made white with lime-based whitewash in 1798, when its walls were finished, simply as a means of protecting the porous stone from freezing. Why the house was subsequently painted is not known. Perhaps presidents objected to the dirty look as the whitewash wore away. The house acquired its nickname early on. Congressman Abijah Bigelow wrote to a colleague on March 18, 1812 (three months before the United States entered war with England):
“There is much trouble at the White House, as we call it, I mean the President’s” (quoted in W. B. Bryan, “The Name White House,” Records of the Columbia Historical Society 34-35 : 308).
The name, though in common use, remained a nickname until September 1901, when Theodore Roosevelt made it official.