Comment: Use canvas' getImageData to get the color rgba value for short time and a bit rough
The following is the source code that requires the browser to support html5<html>
<head>
</head>
<body>
<canvas onmousemove="showCurrentColor(event)">
</canvas>
<br/>
<div>
</div>
<script type="text/javascript">
if(document.createElement("canvas")){
if(document.getElementById("colorPicker").getContext){
var can = document.getElementById("colorPicker");
can.setAttribute("height",300);
var cxt = can.getContext("2d");
var gradient = cxt.createLinearGradient(0.5,0.5,0,150);
gradient.addColorStop(0,'#00ff00');
gradient.addColorStop(1,'#ff0000');
cxt.fillStyle=gradient;
cxt.fillRect(0,0,60,200);
var ox= can.offsetLeft
var oy = can.offsetTop;
var span = document.createElement("input");
span.setAttribute("id","rgba");
document.getElementById("textResult").appendChild(span);
}
}
function showCurrentColor(e){
var x = e.clientX - 8;
var y = e.clientY - 29;
var w = 10;
if(document.createElement("canvas")){
if(document.getElementById("colorPicker").getContext){
var can = document.getElementById("colorPicker");
var cxt = can.getContext("2d");
var gradient = cxt.createLinearGradient(0.5,0.5,0,150);
var span = document.getElementById("rgba");
var imgDatas = cxt.getImageData(ox,oy,10,200);
var imgData = imgDatas.data;
var g = imgData[4 *(w)*(y)+(x)*4 + 1];
var r = imgData[4 *(w)*(y)+(x)*4];
var b = imgData[4 *(w)*(y)+(x)*4 + 2];
var a = imgData[4 *(w)*(y)+(x)*4 + 3];
span.value="r="+r+" g="+ g+" b="+b +" a="+a;
document.getElementById("textResult").appendChild(span);
}
}
}
</script>
</body>
</html>