Grid

def setup():
    size(300, 300)
    background(200)
    lines()

def lines():
    line(100, 0, 100, 300)
    line(200, 0, 200, 300)
    line(0, 100, 300, 100)
    line(0, 200, 300, 200)

def linesAndColour():
    background(160, 32, 240)
    lines()

def draw():
    if (mouseX >= 0 and mouseX <= 100 and mouseY >= 100 and mouseY <= 200):
        linesAndColour()
    elif (mouseX >= 200 and mouseX <= 300 and mouseY >= 100 and mouseY <= 200):
        linesAndColour()
    elif (mouseX >= 100 and mouseX <= 200 and mouseY >= 200 and mouseY <= 300):
        linesAndColour()
    else:
        setup()