Where does the phrase 'vanilla skies' come from?!

Where does the phrase 'vanilla skies' come from?

and what does it mean?
i know its the title of that stupid movie, and its mentioned in the song 'Crush' by Jennifer Paige but i don't know what it means.

http://en.wikipedia.org/wiki/vanilla_sky... is it a tom cruse film in 2001 look at what it
the website dude