[Proyecto] Cambiando de color

<canvas width="600" height="400"> </canvas>

<script>

    var pantalla = document.querySelector("canvas");
    var pincel = pantalla.getContext("2d");    
    pincel.fillStyle = "grey";
    pincel.fillRect(0,0,600,400); 

    let color = ["blue","red","green"];
    let indice = 0;

    function dibujarCirculo(evento){
        var x = evento.pageX - pantalla.offsetLeft;
        var y = evento.pageY - pantalla.offsetTop;    
        pincel.fillStyle = color[indice];
        pincel.beginPath();
        pincel.arc(x,y,10,0,2*3.14);
        pincel.fill();
        console.log(x + "," + y + " " + color[indice]);        
    }

    pantalla.onclick = dibujarCirculo;

    function alterarColor(){
        indice++;
        if (indice >= color.length) {
            indice = 0;
        }
    }

    pantalla.oncontextmenu = alterarColor;

</script>