For such a Northern European country, why are there relatively few true blondes in Ireland?

From everything I've read and seen in person, blondism appears to be rare amongst the indiginous Irish population. The exceptions being people decended from English Protestant settlers and some of the old Norman families. When fair hair is encountered it seems mostly mixed with red to produce a strawberry blonde colour. Unlike most other people from northern Europe, the Irish appear to be overwhelmingly brunette, some even having jet-black hair. Dark, olive skin complections are also more noticeable than you'd expect for this part of Europe.