@classmethod
def rgb(cls, r, g, b, a=255):
    """Convert rgba to KML hex value.

        Args:
          * r: int between 0 - 255 representing red
          * g: int between 0 - 255 representing green
          * b: int between 0 - 255 representing blue
          * a: int between 0 - 255 representing alpha (default 255)
        """
    return '%0.2x%0.2x%0.2x%0.2x' % (a, b, g, r)
