I regularly note the huge difference between London and countryside. Get on a tube and expect a mix, get on a train and it may well be all white. DD noted the same when she went to a predominantly white middle class University.
But it's fine. DDs school friends were racially mixed, Uni friends are different, predominantly northern, many from state schools and some of her closest friends are first generation University. They are a new diversity for her, whilst they have become adept at spotting Londoner differences. (Regular appointments with a dental hygienist is one - who knew.) I think it is great. It is not about her being able to boast of a friendship group of varying hues. It is about her being able to take people as she finds them regardless of colour and background.
Change takes time. Go back a couple of decades and it was very rare to see black or Asian people skiing. A colleague explained. Black people were far too sensible to spend money going somewhere cold when they could have a holiday in the sun. Things are changing, and it is much more common to see mixed families and groups of young people. Ditto the Tooting Lido. Equally I saw colleagues of Nigerian origin start to migrate to market towns in search of cheaper housing.
The pace of diversity will pick up as we have more mixed race families and more secondary migration. And that is ignoring the diversity there already is, including perhaps South Asian Doctors and Chinese restaurant owners, and well as non-visible ethnics including East European farm workers, or the descendants of WW2 refugees. (Lots of Polish names in Cornwall, or the Armenian community in Bournemouth.)
The assumption that racism is the opposite of diversity is flawed.
My family is probably 5 generations London. My dad experienced the post war, no blacks, no Irish, no dogs prejudice. My son risks being accused of white privilege. Integration takes time.