Thanks! The neon element is supposed to be in the ninja himself, he becomes more brightly colored as the game goes on and shoots neon shurikens. The late-game enemies have some neon elements as well, but I agree that fitting the theme is the area where my game struggles the most.
Edit: The enemies used to throw brightly-colored shurikens as well to help the neon theme, but I removed these near the end of the deadline as it caused too much visual clutter.