setBorderAndBackgroundColors(mk) {
    if (mk instanceof Dict) {
      this.borderColor = getRgbColor(mk.getArray("BC"), null);
      this.backgroundColor = getRgbColor(mk.getArray("BG"), null);
    } else {
      this.borderColor = this.backgroundColor = null;
    }
  }
Set the color for background and border if any.
The default values are transparent.

@public
@memberof Annotation
@param {Dict} mk - The MK dictionary