Where did the tall and fair-haired Celts come from?

Celts have brown, black, red or blond hair. The last two would be the fair haired Celts. These variants occur in all Celtic populations from, Spain to Belgium, to the British Isles to France and anywhere else there is a strong Celtic genetic influence. In general Celtic populations are tall. The Britons were wiped out by the Roman and Germanic invasions. Any remnants of Britons would be in what is now Wales. Welsh can be tall, medium or short and dark or light haired.