I don’t mean to call for help just for translation, but I couldn’t find anything related to this word using Google. Dict.cc usually has many alternatives to choose from, for the meaning of a given word. But in this case there was nothing.
The following sentence is the source of it. I read it in Michael Ende’s Die unendliche Geschichte.
... war eine regenfleckige Mauer auf der anderen Straßenseite.
The meaning I can glean from the remaining words is:
… was a wall on the other side of the street.
Does it mean soaked in rain?
fleckigedoesn't help either. The former means
rainI guess, the latter still escapes me.