The original "Celts" who colonized Britain and Ireland probably had dark hair and eyes, i.e. looking more like Central Europeans than like Norsemen.
I thought that the Irish are genetically related to the Spanish. There were obviously waves of tribes pushing west into Europe, with the people at the fringe (Ireland and Spain) most likely to be genetically similar to the earliest groups.
The Romans appeared to have problem distinguishing between Germans, Celts and mixed people (Belgae) by appearance. Read Julius Caesar. So we’re the Cimbri and Teutones Celts or Germans? Or both? I read a book on the Volkerwanderung,translated from German into tortured English. The author maintains that many of these tribes derived their names from the ruling clan of warlords while the rank and file included Celts, Germans, Iranians and Hunt of different tribal origin who continually organized,re-organized, broke apart and reassembled under different chieftains so pigeonholing them by lineage was difficult and in many cases impossible. That may have been the situation here. Ascribing modern views of ethnicity and nationhood to people living in a culture of this period may be flawed in itself.