color b = color(40,60,180);
  color r = color(180,60,40);
  color g = color(205);
 
void setup(){
  size(500,500);
  background(204);
  //Setting up the blue squares
  fill(40,60,180);
  for(int y=0; y<=500; y+=200){
    for(int x=0; x<=500; x+=200){
    rect(x,y,100,100);
    }
  }
  //Setting up the red squares
  fill(180,60,40);
  for(int y=100; y<=500; y+=200){
    for(int x=100; x<=500; x+=200){
    rect(x,y,100,100);
    }
  }
}

void draw(){
  int a; int x; int w; int d;
  if(mousePressed){
   int s = get (mouseX,mouseY); 
   
    if(s==b){       //if you clicked a blue square
      if(mouseX<=100 && mouseY<=100){
      fill(180,60,40);
        rect(0,0,100,100);
      }
    }
    if(s==r){
      rect(103,100,100,100);
    }
  }
}