The discoloration on this page is (like other pages from this issue) a result of the process of putting the issue together properly. This issues villain, -Computrex, the Living Computer- was always a face on a screen, but executed with a pair of surprints, red and blue.
Typically, this would require the space where Computrex's face would be be left blank, and the red and blue elements drawn separately. Gil didn't take that extra step, simply drawing in the face where it should be, requiring editorial to go through a process of taking copies of the surprinted elements before covering them up with white paper on the master page. The stains are a glue residue, as the masks have been removed (thankfully without damage).