Лоэнрон,
<!DOCTYPE html>
<html>
<body>
<canvas id="circle"></canvas>
<script>
var circle = document.getElementById("circle");
circle.width = 256;
circle.height = 256;
var context = circle.getContext('2d');
context.lineWidth = 4;
for(var i = 1; i < 360; i++){
context.beginPath();
context.arc(128, 128, 124, (i-1)*Math.PI/180, i*Math.PI/180, false);
context.arc(128, 128, 0, 0, 1, false);
context.strokeStyle = "RGB(255, "+i+", 0)";
context.stroke();
}
</script>
</body>
</html>