int size = 150;

void setup() {
    size(570, 570);
    noStroke();
    background(220);
}

void draw() {
    int x1 = width / 2 - size / 2;
    int y1 = 105 - size / 2;
    int x2 = x1;
    int y2 = 285 - size / 2;
    int x3 = x1;
    int y3 = 475 - size / 2;
    
    // setze Buttons
    drawButton(x1, y1, color(255, 0, 0), "Rot");
    drawButton(x2, y2, color(0, 255, 0), "Grün");
    drawButton(x3, y3, color(0, 0, 255), "Blau");
    
    // Klick außerhalb der Elemente
    if (!(x1 <= mouseX && 
        y1 <= mouseY && 
        mouseX <= x1 + size && 
        mouseY <= y1 + size) && 
        !(x2 <= mouseX && 
        y2 <= mouseY && 
        mouseX <= x2 + size && 
        mouseY <= y2 + size) && 
        !(x3 <= mouseX && 
        y3 <= mouseY && 
        mouseX <= x3 + size && 
        mouseY <= y3 + size)) {
        
        if (mousePressed) {
            background(220);
        }
    }
}

void drawButton(int x, int y, color paint, String title) {
    // setze Füllfarbe ...
    if (x <= mouseX && 
        y <= mouseY && 
        mouseX <= x + size && 
        mouseY <= y + size) {
        if (mousePressed) {
            background(paint);
        }
        
        fill(200);
    } 
    // setze Rechteck
    rect(x, y, size, size);
    
    // setze Text
    fill(0);
    textAlign(CENTER);
    text(title, x + size / 2, y + size / 2);
    
    
    fill(255);
}