Well, I think there's another question on this matter that needs an answer of anthropology (Valmadian, I don't really know if you have already addressed this subject here in the forum, forgive me if you did). That question is: were the ancient celts so much pale, blond or read headed, as it's commonly said?

Even if they were at the start, I believe that after such a long journey of migration, conquest and settlement, that the celts had probably been through a big deal of morphology changes, apart from the more natural cultural changes. I also believe that the celts of Bretagne could be rather different than the celts from Ireland, for instance.

According to my knowledge of history, no significant iberian presence ever took place in the north-west of the Iberian Peninsula, from where all of my known ancestors were; and yet, I'm as blond as the dark night, as a vast majority of modern galicians and portuguese are. Even considering that the genes responsible for clear eyes and hair are recessive, nothing explains such lack of supposed celtic influence in these peoples modern look... and the same goes for Eire...