Actually Her is an good example of brilliant use of color in films. In my view, this film actually redefined the palette of futuristic films. Earlier films of this genre usually stuck to blue/green palette and this completely broke that stereotype by painting the screen with the exact opposite hue. It brought freshness to the genre. And sure, it did subconsciously implied the passion in the story.
I'm more of an old-school writer. I collect all ideas and jot them down on my notebook. I make maps with them connecting the different ideas with one another and then form the narrative structure out of it. This one really works for me because I want to be able to physically interact with my ideas to make a structure out of it.