This reminds me about the ex-producer of Midsomer Murders who was tackled about the lack of black people on his show. He said, basically, that although Midsomer as a county is fictional, it was based very much on the villages and small towns where it is filmed, namely Oxfordshire and Berkshire, which is almost exclusively white apart from the very large towns and cities. Therefore the series including very, very few black people was accurate.
Unfortunately he didn't choose the best words to say this and he was attacked (rightly, for choice of words) and had to go.
I am nearly 40 and where I live is relatively rural and similar to those counties and if you set a programme here, even in a decent sized town, you'd probably have a cast that was 86.5% white English, 1% white Scottish, 1% white Welsh, 2% white Irish, 2% Asian, 7% white Polish and 0.5% black.
There is definitely a higher percentage of black people on TV now than when I grew up, though. I only ever remember Trevor MacDonald and Lenny Henry from the late-70s and early-80s.
I loved Desmond's too!!!!