Someone's skin color doesn't tell the full story of their ancestry. If there are two northwest European brothers and one has brown skin and one has white skin, do they have totally differnt ancestors? Skin color in a population can change in as little as a few hundred years or a thousand years. The same type of markers that decide whether someone has very dark or very light skin decides whether someone can drink lactose or not, and just 1,000 years ago or so most Europeans could not drink lactose and now almost all can. Skin color can change just as quickly as a population can become immune to a sickness, which we know through history can happen very quickly.
You should define people by their genetic markers not their skin color(unless you sampled 1,000's of them you can only guess). It is hard to give strict definitions to people you can only give general ones, and generally Europeans are defined as being a mixture of two stone age populations; hunter gatherers who lived in or near Europe and farmers who lived in west Asia.
Why European's are uniformly light skinned is a mystery, and it's their genetic markers that define them not a physical trait that can change very quickly. We know through ancient DNA that the hunter gatherers who lived in or near Europe(norther European's main ancestors) probably had dark skin and the farmers from west Asia(south Europeans main ancestors) probably had light skin. We also know that there were genetically modern European(hunter-farmer mix) populations who had dark skin as recently as 5,000 years ago.
Berbers are in no way European, even if they do have light skin.