I pretty much got the idea from the opening clip of the first season. That whole duality theme going on and the conflict inside the main character.
That's pretty much why the use of the black and white on the left ( the human side) . goes with the human good, ghoul bad idea that Kaneki was on at the start. Not sure how much the smile on that side shows dread but that is what I was going for with it and also the sweat and the puppy eyes.
On the colored side is where the details are , the idea being that the ghoul part is more complex that thought before.
Kept the background with the same idea in mind , simple so it wont compete with the character.