I am a strawberry blonde (that is me, by the way). ...
But it definitely does originate from Continental Celt, so regardless the tribes it greatly complicates your Magog hypothesis.
No, it really doesn't. Language can be, and often is, learned. Especially by invading forces who didn't, at first, bring wives and children.
For example, Non-IE Hurrians had IE-Mitanni overlords that used the language of the conquered Hurrian nation. They were not themselves Hurrian, but only Hurrian-speaking.
The Pre-Celtic Tribes of Britain
"We need not, however, go so far as the Pyrenees to find people identical with the
small dark Welsh. The small dark Irish of the south-west of Ireland, the small dark Highlander of Scotland, and the dark inhabitants of Devon and Cornwall are physically of the same race."--Dawkins, Place of the Welsh in the History of Britain
"Solinus ... states that 'a stormy channel separates the coast which the Damnonii occupy from the island Silura, whose inhabitants preserve the ancient manners, reject money, barter merchandise, value what they require by exchange rather than by price, worship the gods, and both men and women profess a
knowledge of the future.'--Skene, Celtic Scotland, v1
"Professor Rhys goes so far as to refer Druidism to the
Silurian race, because Caesar mentions Britain as the birthplace of that cultus, and it is of a character which he considers non-Aryan. It is almost certain that
second-sight and other ecstatic moods must be referred to the
pre-Celtic races."--MacBain, Celtic Mythology and Religion
"Bertrand and Reinach both maintain the
pre-Celtic origin of Druidism."
--Wright, Druidism the Ancient Faith of Britain
"so we must pass on to the
non-Celtic natives, who had another religion, namely,
druidism, which may be surmised to have had its origin among them."--Rhys, Celtic Britain
"The monuments we call
Druidical, must be appropriated, exclusively, to the
Aborigines of the midland, and western divisions. They are found in such corners, and fastnesses, as have, in all ages, and countries, been the last retreat of the conquered, and the last that are occupied by the victorious."--Davies, Celtic Researches
"
The ancient throne was, however, in existence in that part of Wales formerly denominated Siluria, and though its practical authority was curtailed, yet it was genuine and vigorous, and laid claim to all its primitive rights and privileges. Under its protection also flourished Bardism in its native integrity. The correctness of this hypothesis is attested by the unanimous voice of our traditionary documents; and it is remarkable that all those which relate to the doctrine and institutes of the primitive system are invariably written in the Silurian dialect."
--Williams, Ecclesiastical Antiquities of the Cymry
What must be the "Silurian dialect"?
Would blonde or red invaders write the Bardic History called Gododdin?