Image in question is old versions of https://commons.wikimedia.org/wiki/File:Nh-apluto-mountains-plains-9-17-15.png . See also https://commons.wikimedia.org/w/index.php?title=Commons:Village_pump&oldid=172508328#Lost_brighness_after_resizing_png_by_Commons_.28recent_pluto_sunset_photo.29
Compare https://upload.wikimedia.org/wikipedia/commons/archive/c/c3/20150917174614%21Nh-apluto-mountains-plains-9-17-15.png vs https://upload.wikimedia.org/wikipedia/commons/thumb/archive/c/c3/20150917174614%21Nh-apluto-mountains-plains-9-17-15.png/120px-Nh-apluto-mountains-plains-9-17-15.png The thumb appears a lot darker. If you look at metadata, the thumb does not have an icc profile.
Testing locally, I was not able to reproduce this stripping of icc profiles on png files. I believe it is due to different versions of image magick that I have locally vs what wmf uses (I tried 6.6.0-4,6.8.9-3 and 6.9.1-9 locally. The current version on wmf servers appears to be 6.7.7-10 which I don't have installed locally).
This may be a regression from when image scalars were last updated.