An earl of Stamford, the 8th Earl (1812-1890) who succeeded 1883, was married thirdly in 1880 to a Martha Solomon, a lady described as light brown, so probably coloured rather than pure African (daughter of a free slave Rebecca by a man named Solomon from Wellington), in South Africa. Unfortunately, he was a black sheep sent out there in disgrace, and his marriage took place after the birth of some children. So there has been a black countess, who married into an ancient family, no less. (The 8th Earl reformed after his third marriage, and tried to save and earn money to provide for his two children by his third wife).
The 8th Earl left a son John (b 8 October 1877) who married in turn and left a son John (b. 1905) who emigrated to New Zealand. Unfortunately, the son was illegitimate by English common law and peerage law, since Harry Grey didn't marry his housekeeper mistress until Dec 1880. I don't know if there are any descendants of the grandson John Grey. Another daughter Frances Grey (b 29 October 1879; d ca 1883 of smallpox) was also born before the marriage. (Harry Grey's first wife died in 1874, but he didn't remarry until 1880). The legitimate daughter Lady Mary Grey (b 1881) married and divorced an English poet, and had issue 2 sons who were at least 1/8th African, I assume.
If Harry Grey had bothered to marry Martha Solomon(s) before his son's birth, the Stamford earldom might have lasted longer. (Perhaps, he wasn't sure of the whereabouts of his first wife, or whether Martha was free to marry him...)
The 7th Earl of Stamford died without issue in 1883 (his second wife being a bareback circus rider), the 8th Earl married thrice but had issue only by his third wife, the 9th Earl William had one son and one daughter, and the 10th Earl Roger (d 1976) was a recluse who never married.
BTW the widow of the 8th Earl and her children John and Lady Mary Grey and their guardians helped the 9th Earl establish his claim to the earldom in 1892. The 8th Earl himself acknowledged his cousin William (future 9th Earl) as his heir, and stated that his son was illegitimate. There was no counter-claim on John's part, as the 9th Earl was at pains to acknowledge. The Dowager Countess remarried (another Coloured man I believe) and ceased to use the title. John, both illegitimate and mixed-race, was raised in South Africa, while his legitimate sister Lady Mary eventually came to England. I don't know how society would have reacted had the son been legitimate and 9th Earl Grey, instead of his father's cousin
Shinjinee