Plutarch was a Roman citizen of Greek descent who wrote in Greek. The Ancient Greek word for what we'd call black people is μέλας ("dark," from which we derive our word "melanin"). The following story from Plutarch implies that a Roman-era Greek would immediately recognize a black person as foreign.

"For as the warts and moles and freckles of parents, not seen upon the children of their own begetting, many times afterwards appear again upon the children of their sons and daughters; and as the Grecian woman that brought forth a blackamore (μέλαν) infant, for which she was accused of adultery, proved herself, upon diligent inquiry, to be the offspring of an Ethiopian after four generations..."

Herodotus was not Roman but tells an interesting story of some Nasamonian adventurers in the Sahara, who meet some μέλας people. He obviously thinks very highly of these μέλας people.

"They travelled over the desert, towards the west, and crossed a wide sandy region, till after many days they saw trees growing in a plain; when they came to these and were plucking the fruit of the trees, they were met by little men of stature smaller than common, who took them and led them away. The Nasamonians did not know these men's language nor did the escort know the language of the Nasamonians.

The men led them across great marshes, which having crossed they came to a city where all the people were of like stature with the escort, and black (μέλανας). A great river ran past this city, from the west towards the rising sun; crocodiles could be seen in it.​

This is enough to say concerning the story told by Etearchus the Ammonian; except that he said that Nasamonians returned — as the men of Cyrene told me — and that the people to whose country they came were all wizards."