Get the hex color value of an object

Color conversion on Illustrator depends on the color profile setting. The ideal is to let Illustrator convert the colors and use that value.
Here is a POC Code.

var itm = app.selection[0].duplicate();
app.executeMenuCommand("deselectall");
itm.pathPoints[0].selected = PathPointSelection.ANCHORPOINT
app.executeMenuCommand("Colors9");

//get color value

itm.remove()

//send value

You can to get objects color in DOM side ExtendScript and return to Panel JavaScript.

//ExtendScript - get pathItems colour value.
alert(getColorHex())
function getColorHex(){
var tg = app.selection[0];
return "#"+tg.fillColor.red.toString(16)
+tg.fillColor.green.toString(16)
+tg.fillColor.blue.toString(16);
}

//CEP sideJavaScript
var csi = new CSInterface();
csi.evalScript("getColorHex()",function(ev){alert(ev)})