The bark of some _pinus_ species, like _pinus sylvestris_ and _pinus pinaster_ naturally turns orange when they are a bit older. Other species stay grayisch black, like _pinus nigra_ (hence the name).
By the way: I have never seen _pinus sylvestris_ grow so straight. Is it possible this is another species, for example P. pinaster?
Sources: Den nya nordiska floran (Mossberg&Stenberg 2003) and Heukels' flora van Nederland (van der Meijden 2005).