Another exploration we can achieve with nested loops is to generate interesting textures by using mathematical operators like the modulo, which allows us to create a smooth transition between colors. A very basic, but visually appealing example.

void setup() {
  size(600, 400);
}

void draw() {
  background(0);
  noStroke(); 

  int step = 40;

  for (int i = step; i < width; i += step) {
    for (int j = step; j < height; j += step) {
      fill(i % 255, j % 255, 150); 
      print("R:" + str(i%255)+ "G:" + str(j%255));
      ellipse(i, j, 35, 35);
    }
  }
}