The Normans replaced the Britons who were darker
The Welsh are the only dark people left on the Isles and even they aren’t homogeneous in that anymore
I can’t even tell if you’re talking about Brittany or England. The Normans pushed out the Celtic bretons in Brittany but that has nothing to do with the isles where the West Germanic angles and Saxons pushed out the native Celtics. There the Normans just came up to rule.
England
Britain is because Rome called the people that lived there Britons
Predating Brittany
Then the Normans did not replace anybody in England other than rulers. The angles already did that, thus “angle land.” The Normans pushed out the bretons in Brittany, or northern France.