In answer to my question ‘why is Pluto reddening?’ I got some information about a NASA site that gives a possible explanation, here it is:
“These changes are most likely consequences of surface ices sublimating on the sunlit pole and then refreezing on the other pole as the dwarf planet heads into the next phase of its 248-year-long seasonal cycle. The dramatic change in color apparently took place in a two-year period, from 2000 to 2002.”
I also read that taking good pictures of Pluto is not at all simple. One astronomer said it is like taking a photo of a soccer ball from about 70 km away.