Yep. Also there are late medieval paintings that show black people living in Europe that aren't just like a "blackface style." They are pretty clearly African based on the facial features, hair etc.

Or remind them that one of the people shot in the Boston Massacre, and it is depicted in the most famous contemporary image of it, was a black dude.

What is also interesting is there is a medieval european painting of a battle between the Christian Ethiopians and Muslims and they depict the Ethiopian soldiers as wearing European style armor. Which was probably not the case irl. But it gets the point across to the ignorant which side to cheer for if you were a European Christian.