CompareColorValues.js

for (var k = 0; k < sharedStyles.numberOfSharedStyles(); k++){
  var layerStyle = sharedStyles.objects().objectAtIndex(k);
  var styleName = String(layerStyle.name());

  //checks if the name of the imported color is the same as the existing
  if(styleName == colorName){

    var fill = layerStyle.value().fills().firstObject();
    var oldFill = String("#" + fill.color().immutableModelObject().hexValue());

    //checks if the existing color value is different than the imported one
    if(oldFill != colorValue){
      //change the fill color of the shared style
      fill.color = colorFromString(colorValue);
      //create a color to be added to the Document colors
      var color = colorFromString(colorValue);
    }
  }
}