Set_All_Track_Matte_Label.jsx

/**
 * @name Set All Track Matte Labels
 * @version 2.1
 * @author Kyle Martinez <www.kyle-martinez.com>
 *
 * @description Set the label color for all track matte layers in the active composition to "16". In
 * my preferences label 16 is Black "#000000" and is always used for track mattes.
 *
 * @license This script is provided "as is," without warranty of any kind, expressed or implied. In
 * no event shall the author be held liable for any damages arising in any way from the use of this
 * script.
 *
 * I'm just trying to help make life as an After Effects animator a little easier.
 */

(function setAllTrackMatteLabels() {
    app.beginUndoGroup("Set All Track Matte Label(s)");
    var comp = app.project.activeItem;
    var layers = comp.layers;
    for (var l = comp.numLayers; l > 0; l--) {
        var layer = layers[l];
        layer.label = (layer.isTrackMatte) ? 16 : layer.label;
    }
    app.endUndoGroup();
})();