int size = 150; // Durchmesser

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

void draw() {
    // setze Buttons
    drawButton(width / 2, 105, color(255, 0, 0), "Rot");
    drawButton(width / 2, 285, color(0, 255, 0), "Grün");
    drawButton(width / 2, 475, color(0, 0, 255), "Blau");
    
    // Klick außerhalb der Elemente
    if (dist(mouseX, mouseY, width / 2, 105) > size / 2 && 
        dist(mouseX, mouseY, width / 2, 285) > size / 2 && 
        dist(mouseX, mouseY, width / 2, 475) > size / 2) {
        
        if (mousePressed) {
            background(220);
        }
    }
}

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