At http://phys.org/print363535162.html … it seems that Pluto has blue skies, just like the Earth. It also has patches of frozen water – and both are a surprise.
On Earth blue skies are seen because of the scattering of sunlight by nitrogen particles – so why the blue skies on Pluto?
The water ice appears to be where the planet is shaded a rdder colouration. Why is water ice ruddy? However, see www.spaceweather.com October 9th 2015