I agree with that. Britons would have regarded Berbers as swarthy and dark. But wardaddy is also correct when he says that Old King Cole’s name is derived from the Celtic word meaning ‘coil’ and has no relation to ‘coal’. He was more likely a native Briton than a Berber brought along by the Roman legions. Britons were a clannish people. Their descendants in America still are. It’s a stretch to think that an outsider would lead them.
Wikipedia notes that King Cole was possibly a Briton who had been a leader in the Roman military, who had turned his command into a kingdom when Rome left.
This same scenario is suggested for King Arthur- a Romanized Briton, a cavalry officer who attempted to maintain Roman civilization after the legions pulled out.
This is even more true in Old King Cole's case since he predates the legendary King Arthur by a couple of centuries.
The native Brits certainly had no love for the Romans up to and including Boudicca's time and for several years beyond.
By the time Arthur's legend rolled around, they had grown so fond of things Roman that the Roman founded city of London became their capital.
Even as late as the Elizabethan age, portions of the original Roman wall were still intact within London and the English had come to see themselves as the key preservers of civilization exemplified by Roman culture, even though Elizabeth's father had made every attempt to stamp out the Roman Catholic church, arguably history's greatest repository of the same.
The point, I suppose, is that a lot changes in a relatively short time and legends change and metamorphisize to fit the needs of the purveyors of those same legends.