18th century antiquarians like Charles Vallancey speculated that Irish civilization was founded by Phoenician seafarers, and attempted to prove this using what we would call today linguistic arguments. While largely discredited, it is possible that Carthaginian explorers based in present-day Morocco sailed north on voyages of trade and exploration. Pliny describes an expedition led by Himilco from Gibraltar to the islands north of mainland Europe. Details are sparse, unfortunately. I am not aware of any archeological evidence of continuous direct trade between Ireland or even Britain and the Mediterranean world. The commodity of the area most valued, tin, appears to have likely been transported across present day France via a series of Celtic middle-men.

The Fragmentary Annals of Ireland contain a passage describing the adventures of a band of vikings who sailed south to Iberia and then crossed into Africa:

Then their arrogance and their youthfulness incited them to voyage across the Cantabrian Ocean (i.e. the sea that is between Ireland and Spain) and they reached Spain, and they did many evil things in Spain, both destroying and plundering. After that they proceeded across the Gaditanean Straits (i.e. the place where the Irish Sea sic goes into the surrounding ocean), so that they reached Africa, and they waged war against the Mauritanians, and made a great slaughter of the Mauritanians. However, as they were going to this battle, one of the sons said to the other, ‘Brother,’ he said, ‘we are very foolish and mad to be killing ourselves going from country to country throughout the world, and not to be defending our own patrimony, and doing the will of our father, for he is alone now, sad and discouraged in a land not his own, since the other son whom we left along with him has been slain, as has been revealed to me.’ It would seem that that was revealed to him in a dream vision; and his Ragnall's other son was slain in battle; and moreover, the father himself barely escaped from that battle—which dream proved to be true.

While he was saying that, they saw the Mauritanian forces coming towards them, and when the son who spoke the above words saw that, he leaped suddenly into the battle, and attacked the king of the Mauritanians, and gave bim a blow with a great sword and cut off his hand. There was hard fighting on both sides in this battle, and neither of them won the victory from the other in that battle. But all returned to camp, after many among them had been slain. However, they challenged each other to come to battle the next day.

The king of the Mauritanians escaped from the camp and fled in the night after his hand had been cut off. When the morning came, the Norwegians seized their weapons and readied themselves firmly and bravely for the battle. The Mauritanians, however, when they noticed that their king had departed, fled after they had been terribly slain. Thereupon the Norwegians swept across the country, and they devastated and burned the whole land. Then they brought a great host of them captive with them to Ireland, i.e. those are the black men. For Mauri is the same as nigri; 'Mauritania' is the same as nigritudo. Hardly one in three of the Norwegians escaped, between those who were slain, and those who drowned in the Gaditanian Straits. Now those black men remained in Ireland for a long time. Mauritania is located across from the Balearic Islands.

But I doubt that this had any significant impact on Irish genetics. The 'black Irish' have probably existed in Ireland since the Neolithic, since there haven't been any substantial changes to the Irish genetic makeup since that period. Geneticist Brian Sykes has suggested that the Neolithic colonists of both Britain and Ireland originated in Iberia on the basis of his analysis of Irish and British mitochondrial DNA, so it's safe to say that dark hair and relatively swarthy complexions are indigenous to Ireland and not the result of shipwrecked sailors or African slaves intermarrying with the island's inhabitants.