static createDefaultCue(startTime, endTime, payload) {
    const cue = new shaka.text.Cue(startTime, endTime, payload);
    cue.color = shaka.cea.CeaUtils.DEFAULT_TXT_COLOR;
    cue.backgroundColor = shaka.cea.CeaUtils.DEFAULT_BG_COLOR;
    return cue;
  }
Returns a cue with no underline/italics, and default colors
@param {number} startTime
@param {number} endTime
@param {string} payload
@return {!shaka.text.Cue}