Arrow writers are using colors this season to give Olicity shippers hope. From episode one of Arrow's third season the color red has been used to signify the relationship between Oliver Queen and Felicity Smoak. The more they stray from the possibility of a working relationship between the two characters, the more hints keep popping up.
First a little back story for those that don't know what I'm talking about. "It was red" is from Oliver and Felicity's first date in episode 3x01. Felicity is embarrassed about the pen she was chewing on when they first met and Oliver surprises her by remembering that it was a red pen. Where she felt he never paid her much attention, we've come to learn he remembers every detail about her and has from the beginning.
In the most recent episode of The Flash the stars of Arrow cross universes. While the hero's are out fighting, Felicity has an interesting conversation with the character Caitlin Snow about color psychology. Felicity defines it as "the theory that changes in the color spectrum can effect emotion."
Now that Olicity's romantic relationship is on the rocks, blue is being used to signify Felicity's interest in Ray Palmer. The company's color is blue, the dress he loans her is blue, and she's wearing blue while discussing color psychology. The writers are placing Felicity in blue more and more to show us that she is refusing to deal with the yo-yoing she and the audience have been subjected to from the start.
In episode 3x07, John Diggle visits Felicity in her office to tell her how Oliver is being affected by her relationship with Palmer. The blue dress looms over them in the background during their discussion, but if you look carefully, you'll see a red pen on Felicity's desk. I believe this is the writers way of telling the audience that Palmer might be who she is interested in at the moment, but Oliver is not far from her thoughts. A dress is used for an evening. A pen is used everyday.