javascript color green to red
function perc2color(perc) {
var r, g, b = 0;
if (perc < 50) {
r = 255;
g = Math.round(5.1 * perc);
}
else {
g = 255;
r = Math.round(510 - 5.10 * perc);
}
var h = r * 0x10000 + g * 0x100 + b * 0x1;
return '#' + ('000000' + h.toString(16)).slice(-6);
}