*Actually the appearance of people that are called "celtic types" in the anglo-saxon modern use of description is pictish rather than gaelic.

*Ermmm...  Since we don't know what the "Picts" looked like (beyond the likelihood that they did not paint themselves blue), that's pretty speculative.   I already alluded to the current belief that the Irish and Angle invasions (and, for that matter, the Danish and Norman invasions) didn't make a huge dent in the indigenous DNA in Britain.   "Gaelic" and "Celtic" aren't racial terms, but primarily linguistic;  Breton and Welsh are "Celtic", without being "Gaelic", and a man's ability (or inability) to speak Breton tells you nothing about his appearance.

*I always though 'woad' was the substance they used to paint their bodies blue.

*Yep, it has a yellow flower, but produces a blue dye.  I bet that gave them a surprise, the first time they tried it.