In the film we see that a black man in a noble in queen Elizabeth's court is it accurate that black people were given such high positions or is it just to diversify the caste of the movie
*Adapted from a previous answer
Some Europeans courts did have African servants. The best known example is John Blanke, a black musician who went to England with Catherine of Aragon and later worked for Henry VIII, becoming a relatively well-known member of Henry's entourage.
However, all the titled nobility and virtually all of the servants in European courts were European.
Why does the movie present something different? The makeup of Mary and Elizabeth's courts was a deliberate and explicit artistic choice on the part of director Josie Rourke. Rourke has explicitly said as much:
“I was really clear, I would not direct an all-white period drama. Adrian [Lester], who plays, Lord Randolph, grew up 40 miles from the birthplace of William Shakespeare; he is one of our eminent Shakespearean actors. I needed to cast an ambassador who could move between the two courts and help this make sense. I don’t understand why you wouldn’t cast him.”
Rourke's position lead to some casting choices where the courts of Mary and Elizabeth look less racially homogenous than they actually were. Of course" Mary and Elizabeth's courts (Mary's in particular) were quite diverse in terms of nationalities - there were courtiers from all over Europe.
As a result of Rourke's choices, many actors in the film don't resemble historical people they're playing (not that this is admittedly a new phenomenon in Hollywood!)
The ambassador "Lord Randolph" Rourke mentioned earlier is based on Thomas Randolph, one of Queen Elizabeth's secret agents and ambassadors. As far as I know there's no known portraits of him - however, he wasn't of African origin or even mixed-race.
Adrian Lester as "Lord Randolph"
Bess of Hardwick (aka Elizabeth Cavendish, aka Elizabeth Talbot, Countess of Shrewsbury) was an English courtier and noblewoman. She's played by a Briton of Chinese ancestry, Gemma Chan.
Gemma Chan as Bess of Hardwick
One of Mary's companions, Lady Mary Seton, was born to a Scottish father and a French mother.