There references in Celtic myth to copper skinned brothers, and a land of grapes bounded by wasteland of ice and snow, which ended in a great flood forcing the Tuatha to travel towards the rising sun to Ireland.

It is also a point that the classic Celtic colouration [fair-skinned, pale, red hair, blue or green eyes] is better adapted to a forest environment... and Ireland as well as most of the celtic heartland isn't all that deeply forested, nor hasn't been for a very long time.

I think, suspect, that the true celtic homeland was America, about where the great lakes are now. That the ancestors of the Native Americans originally lived further south, and moved north after the end of the ice-age.