I suspect that I may be conflating a couple of different books that I've read, but I'm looking for a short story collection that I read in the late 1970's, early 1980's.
Items that I remember:
- Cover was..purple? With two or three triangle shapes on it, slightly overlapping (They correlate to one of the stories)
- I think the title is similar to Year's Best Science Fiction or along the lines of "Best of" or similar (I have been through all the Years Best covers on the wiki site)
- One short story that I definitely remember being in the book is Rain Rain Go Away by Asimov, but I've been through all the related books and covers at the ISFDB. (This may be conflated, but I really remember it being in the book)
- The story with the triangle shaped creatures, they may have been two dimensional? IIRC they were either observing or being observed? They may have been purple while the cover was a different color, but purple was involved.
It was definitely in English, cover art that I remember was typical for the time, possibly slightly more dated (So similar to 1960's early 1970's cover art/fonts), paperback version.