black & white

int
    y, // joint height of the figures
    squareX, // x of the square
    circleX, // x of the circle
    size, // joint size (diameter) of the figures
    squareColor = 0, // square color
    circleColor = 255, // circle color
    baseColor = 100; // background color

void setup() {
    size(1280, 745);
    rectMode (CENTER);

    size = height / 4;
    y = height / 2;
    squareX = width / 2 - size;
    circleX = width / 2 + size;
}

void draw() {
    // background
    if (overSquare())
        background(squareColor);
    else if (overCircle())
        background(circleColor);
    else
        background(baseColor);

    // square
    stroke(circleColor);
    fill(squareColor);
    square(squareX, y, size);

    // circle
    stroke(squareColor);
    fill(circleColor);
    circle(circleX, y, size);
}

boolean overSquare ( ) {
    int radius = size/2;
    if (mouseX >= squareX - radius && mouseX <= squareX + radius
        &&
        mouseY >= y - radius && mouseY <= y + radius
    )
        return true;
    else
        return false;
}

boolean overCircle ( ) {
    if (sqrt(sq(circleX - mouseX) + sq(y - mouseY)) < size/2)
        return true;
    else
        return false;
}