int i = 0;
int x = 10;

void setup() {
   size(600,600);
   background(0);
}

void draw() {
  frameRate(5);
  for(int a = 15 ; a < 585 ; a = a + 20) {
    for(int i = 15 ; i < 585 ; i = i + 20) {
      fill(0,random(0,200),random(0,200));
      noStroke();
      rect(i,a,10,10);
    }
  }
}
//╮( ˘_˘ )╭
void mousePressed (){
  fill(random(0,200),0,random(0,200));
  redraw();
}