From my experience the multi colored sections on the inside usually have a method to the madness. Like green bits on one side and red on the other which helps during assembly. They like to rotate the model a bunch in the instructions and it gives you some reference points. I’m sure some of it is cost savings as well. They just use whatever the most common color is for the brick. I agree with most of the other points. You definitely have to pick and choose the sets that are worth it.