size(400, 400);

background(250);

stroke(0) ; 

strokeWeight(5);

line(100,0 , 100, 400);

line(0, 100, 400, 100);

fill(255,0,0);

rect(0,300,100,100);

fill(255, 255, 0);

rect(0,0, 100, 100);

fill(50,0,100);

rect(0,250,100,50);