Mi version

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

<script>

    var colores = ["blue","red","green"];
    var pantalla = document.querySelector("canvas");
    var pincel = pantalla.getContext("2d");
    var colorActual  = colores[0]   

    pincel.fillStyle = "grey";
    pincel.fillRect(0,0,600,400); 


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

    pantalla.onclick = dibujarCirculo;

    function alterarColor(evento) {

        var indiceColor = colores.indexOf(colorActual);
            if (indiceColor === colores.length - 1) {
                colorActual = colores[0];
            } else {
                colorActual = colores[indiceColor + 1];
            }
        return false;

        pincel.fillStyle = colorActual;

        console.log(colorActual);

    }

    pantalla.oncontextmenu = alterarColor;



</script>  
![Se guarda valores en la consola](https://cdn1.gnarususercontent.com.br/6/554478/fd732183-b868-4e11-9bad-ddb0c6ecb2f9.jpg)