CODE EXAMPLE FOR JAVASCRIPT

convert rgb value in hexadecimal system

    function convertRgb(rgb) {
  // This will choose the correct separator, if there is a "," in your value it will use a comma, otherwise, a separator will not be used.
  var separator = rgb.indexOf(",") > -1 ? "," : " ";


  // This will convert "rgb(r,g,b)" into [r,g,b] so we can use the "+" to convert them back to numbers before using toString 
  rgb = rgb.substr(4).split(")")[0].split(separator);

  // Here we will convert the decimal values to hexadecimal using toString(16)
  var r = (+rgb[0]).toString(16),
    g = (+rgb[1]).toString(16),
    b = (+rgb[2]).toString(16);

  if (r.length == 1)
    r = "0" + r;
  if (g.length == 1)
    g = "0" + g;
  if (b.length == 1)
    b = "0" + b;

  // The return value is a concatenation of "#" plus the rgb values which will give you your hex
  return "#" + r + g + b;
}