Canvas tint color

HTML

<!--[if IE]>
            <script type="text/javascript" src="http://explorercanvas.googlecode.com/svn/trunk/excanvas.js"></script>
        <![endif]-->
        <!--[if lt IE 9]>
            <script src="http://html5shim.googlecode.com/svn/trunk/html5.js"></script>
        <![endif]-->

<canvas id="myDrawing" width="770" height="400">
            <p>Your browser doesn't support canvas.</p>
        </canvas>

JavaScript

var x; //drawing context
                var width;
                var height;
                var fg;
                var buffer
                
                window.onload = function() {
                    var drawingCanvas = document.getElementById('myDrawing');
                    // Check the element is in the DOM and the browser supports canvas
                
                    if(drawingCanvas && drawingCanvas.getContext) {
                        // Initaliase a 2-dimensional drawing context
                        if (typeof window.G_vmlCanvasManager!="undefined") { 
                            drawingCanvas=window.G_vmlCanvasManager.initElement(drawingCanvas);
                            var x = drawingCanvas.getContext('2d');
                        }else{
                            var x = drawingCanvas.getContext('2d');
                        };
                        
                       // x = drawingCanvas.getContext('2d');
                        width = x.canvas.width;
                        height = x.canvas.height;
                
                        // grey box grid for transparency testing
                        x.fillStyle = '#666666';
                        x.fillRect(0,0,width,height);
                        x.fillStyle = '#AAAAAA';
                        var i,j;
                        for (i=0; i<100; i++){
                            for (j=0; j<100; j++){
                                if ((i+j)%2==0){
                                    x.fillRect(20*i,20*j,20,20);
                                }
                            }
                        };
                
                        // create offscreen buffer, 
                        buffer = document.createElement('canvas');
                        if (typeof window.G_vmlCanvasManager!="undefined") { 
                            G_vmlCanvasManager.initElement(buffer);
                            var bx = buffer.getContext('2d');
               ...