gradation2.pde

size(200, 200);
colorMode(HSB, 100);
background(99);
noStroke();

int i;
for (i = 0; i <= 3; i = i + 1) {
  fill(45, 80 - 20 * i, 99);
  rect(0, 0, 200 - 50 * i, 200 - 50 * i);
}