How to explain the colour of these scots pines?
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&amp;Stenberg 2003) and Heukels' flora van Nederland (van der Meijden 2005).