size(510, 510);

ellipseMode(CORNER);
noStroke();
background(255);


for (int row=0; row<10; row++ )
  for (int col=0; col<10; col++)
  {
    float r = random(255);
    float g = random(255);
    float b = random(255);

    fill(r,g,b);
    rect(5 + 50 * col, 5 + 50 * row, 50, 50);
    fill(255-r,255-g,255-b);
      ellipse(10 + 50 * col, 10 + 50 * row, 40, 40);
  }