Picture the knights of the round table. They’re probably tall and strong, wearing armor and drinking out of chalices. And they’re probably all white. And while most of that picture is relatively accurate, the whiteness is not. Meet Sir Morien, the black knight of the round table. 
The blog MedievalPoC points out that Morien has been largely forgotten or white-washed in modern depictions of the round table. But early texts describe him pretty clearly as not-white. The blog quotes from the translated saga of Morien:
He was all black, even as I tell ye: his head, his body, and his hands were all black, saving only his teeth. His shield and his armour were even those of a Moor, and black as a raven…
Had they not heard him call upon God no man had dared face him, deeming that he was the devil or one of his fellows out of hell, for that his steed was so great, and he was taller even than Sir Lancelot, and black withal, as I said afore…
When the Moor heard these words he laughed with heart and mouth (his teeth were white as chalk, otherwise was he altogether black)…
Morien isn’t even the only knight who isn’t white in the Arthurian folklore as the blog Elodie Under Glass points out:
First off, six percent of the Knights of the Round Table were men of color. Granted, that’s only three out of 49 men, but the entire expanded United States Congress is hovering around 13% people of color and only has one black Senator. 
Although, it's worth noting, one of those three men is green. But he’s definitely not white. So why do all our modern renditions of the round table include a team of totally white guys? Well, not every version of the round table stories points out specifically that Morien is black. Elodie Under Glass explains:
Meanwhile, characters in these stories aren’t really visually described unless they have superlative characteristics, such as mysterious all-black armor or remarkably long golden hair. Many knights were described as dark in hair and features. Instead of placing a large flashing sign in the middle of a saga going “THIS PERSON IS TOTALLY A PERSON OF COLOR YOU GUYS, WE REALLY HOPE YOU WILL TAKE THIS INTO ACCOUNT IN FUTURE ADAPTATIONS” the narrative might well have said “Sir Bors, who was dark” and moved on, assuming that readers or listeners would interpret it the way the narrator meant.
So the storytellers assumed we’d be sharp enough to pick up on their hints that Morien was black. Turns out, we’re not. And the West prefers white heroes anyway. So we now get a round table of white men.