I always lay my blocks out on the board and then back away and do the "squint test" where you close your eyes almost all the way which magically allows you to see your variations of dark/light. When I do that with yours I see a defined line of dark in column #1 and also in column #5. So for me, I would try to break up that color definition a little bit. You did a great job on the curves by the way !!!