Almost throughout my teaching career there was a need in the people who ran the show to find the right balance in the material we delivered to the children. Some of that was in religion and eventually various models for the delivery of a comparative religious format. Later there was a similar movement in the delivery of English but it never really materialised across the whole educational estate. In researching the subject there were plenty of instances of people from a variety of ethnic backgrounds that have written excellent works but still the system resisted the change from white middle class male writers. It has taken a long enough time to include the works of female writers and yet there are some great words from Asian and black writers out there.
Dr Harold Moody
One of the main educational points of having significant people from a variety of ethnic backgrounds is so that children of a similar ethnicity can identify with them and feel included.
Dr Moody was a physician who came to England at the end of the 19th century but was refused work because of his ethnicity and so started campaigning against prejudice. Although he wasn't a writer he was a significant individual whose life and work are worthy of study.
Samuel Coleridge-Taylor (15 August 1875 – 1 September 1912) was an English composer of part Creole descent who achieved such success that he was once called the "African Mahler". Samuel was most widely known for his work The Song of Hiawatha but he also composed and produced an opera which is in the British Library and written in his own hand.
Walter Tull was a professional footballer who played for Tottenham Hotspurs and Northampton Town. He joined the army and fought in the First World War and was the first black officer leading white soldiers. He died in battle in 1918.
Mary Jane Seacole (née Grant; 1805 – 14 May 1881) was a Jamaican woman of Scottish and African descent who set up a "British Hotel" behind the lines during the Crimean War. She described this as "a mess-table and comfortable quarters for sick and convalescent officers", and provided succour for wounded servicemen on the battlefield. She was posthumously awarded the Jamaican Order of Merit in 1991. In 2004 she was voted the greatest black Briton.
So four black people who have made the top 100 Black Britons list and who have had biographies produced about their lives.
It is difficult enough producing stories and so maintaining an ethnic balance could make the story more complicated than it needs to be, but there is no harm in having characters of different ethnicities. It could make your story more appealing to a wider social group.