code: def normalize_hex(hex_color):
      
      hex_color = hex_color.replace('#', '').lower()
      length = len(hex_color)
      if length in (6, 8):
          return '#' + hex_color
      if length not in (3, 4):
          return None
      strhex = u'#%s%s%s' % (
          hex_color[0] * 2,
          hex_color[1] * 2,
          hex_color[2] * 2)
      if length == 4:
          strhex += hex_color[3] * 2
      return strhex
docs: Transform a xxx hex color to xxxxxx.