Just as I thought when I asked the question, they are softwood windows and yes, softwood windows will turn black after a few years. The only option is to paint.
Everyone wants the lovely light pine colour but it will only last a few years no matter how well you care for it. I was looking at a lovely building in Kilkenny a few weeks ago which has pine colour windows from another well know company and they are only in the building 4 years max and they had turned black at the bottom, last week and I passing they were painting them red.
Hardwood is the only answer for outdoor joinery.