Proyecto

<meta charset="utf-8">
<canvas width="600" height="400"> </canvas>
<script>



    var pantalla = document.querySelector("canvas");
    var pincel = pantalla.getContext("2d"); 
    var colores = ["blue","red","green","yellow","grey"];
    var indiceColor = 0;
    pincel.fillStyle = "pink";
    pincel.fillRect(0,0,600,400); 



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

    pantalla.onclick = dibujarCirculo;

    function alterarColor() {
        indiceColor ++;
        if (indiceColor >= colores.length) {
            indiceColor = 0;
        }


        alert("Funcionó: " + colores[indiceColor]);
        return false;
    }


    pantalla.oncontextmenu = alterarColor;