Blue Skies, Some Rain.
As for the “meaning” of it, the meaning is whatever you want to give it! This morning I looked up the meaning of “blue sky” on the web and was amazed to find that there are some negative meanings, not to mention many more songs than the one I remembered, mostly songs with positive meanings.
For me, it just means: there are blue skies, and there is rain! Sometimes one, sometimes the other, sometimes both at once or both in a day. (And when skies are grey too long, I try to remember that rain is needed, and blue sky will return!)