Get a lighter / darker shade

get_shade.js

var get_hex = function(i) {
  i = Math.round(i);
  if(i>255) return 'ff';
  if(i<0) return '00';
  i =i .toString(16);
  if(i.length==1) i = '0'+i;
  return i;
}

var get_shade = function(color, factor) {
	if(color.substr(0,3)=="rgb") {
		var rgb = function(r,g,b) {
			return get_hex(r) + get_hex(g) + get_hex(b);
		}
		color = eval(color);
	}
	var get_int = function(hex) {
		return parseInt(hex,16); 
	}
	return get_hex(get_int(color.substr(0,2)) * factor)
		+ get_hex(get_int(color.substr(2,2)) * factor)
		+ get_hex(get_int(color.substr(4,2)) * factor)
}