The running theory for the traffic lights, and I've examined this closely and it really seems to match up, is this...the light changes depending on James Hurley's emotional state. And James is the suckeyest little suck that's ever sucked, so they change often. Red for when he's angry, green for when he's at peace with the world, and yellow for when he's depressed or in some other emotional state.
Oh, and red, yellow, or green for when he sucks.