This isn't really a theory about the Sides, more about why Thomas chose one of the colours for a Side.

So, Thomas is a theatre kid. I'm pretty sure that's well established. What colour is unlucky in the theatre? Green. Which Side wears green? Remus. Why is this important? Well, Remus is (obviously) intrusive thoughts which could be described as 'unlucky' or are thoughts that show up at 'unlucky times'. Prove me wrong with this colour theory. (please don't actually, I don't exactly want an argument in the comments.)

Please tell me what you think of this insanely short theory in the comments.
Bye,
Queenie