You need to be new to a place to be struck by the obvious. The first thing I noticed about Washington, DC, wandering around the city as a wide-eyed neophyte last autumn, was its astonishing, almost blinding whiteness. The White House really is white, from its balustrades to its basement – at least on the outside. It is in fact constructed of light brown Aquia Creek sandstone from Virginia, but this was whitewashed for the first time in 1798, and then the temporary whitewash was replaced with successive layers of white lead paint. It was the white paint that gave the house its name, which only became official under Theodore Roosevelt in 1901.

A couple of miles east, on its little hill, the shining white Capitol looks down along the Mall and on a succession of white marble monuments, museums and memorials: the magnificent, 550-foot needle obelisk of the Washington Monument, the neoclassical National Gallery of Art and, at the far end of the Mall, close to the Potomac, the white Doric grandeur of the Lincoln Memorial.

Is any other city in the world quite so white? St Petersburg could be a candidate, though the façades of the Winter Palace and other buildings along the Neva are varied with green, pink or gold. And there is Brussels, which struck Marlow, returning from the horrors of the Belgian Congo in Conrad’s

Heart of Darkness, as “a whited sepulchre”.

Aesthetically, Washington’s whiteness is rooted in the theory and practice of European neoclassicism first enunciated in the 1760s by the art historian Johann Joachim Winckelmann. Winckelmann loved classical, and especially Greek, art and architecture for their “noble simplicity and quiet grandeur”. For Winckelmann, a critical component of that simplicity and grandeur was whiteness. His theories influenced such neoclassical architects as Robert Adam; neoclassical canons crossed the Atlantic and impressed the founders and architects of the new republic, including Thomas Jefferson and Pierre Charles L’Enfant. Not long after Winckelmann, other scholars and archaeologists, beginning with Antoine-Chrysostome Quatremère de Quincy, began to point out that much Greek sculpture was brightly coloured. Even the Parthenon would originally – at least on the inside – have been a riot of colour.

So is Washington’s noble and inspiring whiteness built on a misconception, or a lie – or even a series of lies? Whiteness, of course, is not just a matter of aesthetics or architecture, marble or white lead paint. It is unavoidably symbolic as well as real.

Washington, demographically, is far from being a white city. It had a large majority-black population from the 1950s until 2011. The most recent figures show the racial breakdown as follows: 47 per cent black, 36 per cent white, 11 per cent Hispanic. What is striking is not just that many more black than white people live in Washington; it is also where they live. North-west Washington, where most of the monuments and museums, and the historic district of Georgetown, are located, and where most tourists are happy to be confined, is predominantly white. With gentrification, which is also to some extent a whitening process, formerly largely black areas such as Shaw (the home of Howard University, alma mater to so many of Washington’s black intellectuals, movers and shakers) are less black than before.

Many of the buildings here burned during the riots that followed the murder of Martin Luther King in 1968. Further south and east, the Anacostia River marks an unwritten divide between white and black Washington; housing segregation was in force until the 1960s. Rather scandalously, the maps in my very white-looking Dorling Kindersley travel guide stop at this boundary.

This impression of the whiteness of Washington was followed by another. Maybe, I found myself thinking, as I began to assimilate not just the visual impact of buildings but the hum and patterns of voices, of looks and smiles and gestures and conversations and street music, this is a city – the city of Duke Ellington – whose soul is black.

Do all those white marble monuments feel ever so slightly cold? Well there’s a new kid on the block, or rather the Mall: the Smithsonian Institution’s National Museum of African-American History and Culture, a three-tiered glass structure (designed by the Ghanaian-British ­architect David Adjaye) faced with delicate, dark-bronze-coloured aluminium panels, which opened in September. It has proved such a success that it’s almost impossible to get in.

This is a museum constructed as an experiential narrative, and a pretty overwhelming one at that. You start below ground, in an underbelly of deathly slave ships, markets of human flesh, children’s shackles. The journey goes tortuously towards the light, through organised resistance, civil war and abolition; the horrors of Jim Crow laws, lynchings and segregation; yet more concerted and heroic resistance, the civil rights movement. An apotheosis comes with the election, and re-election, of Barack Obama.

As I emerged back on to the Mall, chastened and uplifted by so many stories of resistance to dehumanisation, I realised there is no uninterrupted march of progress; history is dialectical, not linear. Now there is a new, white president in the White House. This week, after many false starts, the White House said Donald Trump would visit the museum. Yet his closest adviser, Stephen Bannon, flirts openly with the language of white supremacism. Musing last year about police killings of unarmed black people, Bannon offered an explanation that can only be construed as profoundly racist: “There are, after all, in this world some people who are naturally aggressive and violent.”

If the White House is supposed to symbolise “a repository of democratic aspirations, high principles and ethical values”, as Clarence Lusane puts it in The Black History of the White House, then it looks as if black people, in the capital and throughout the United States, may once again be called upon to “make the nation live up to the egalitarian and liberationist principles expressed in its founding documents”.