title: finding out complementary/opposite color of a given color
body: <p>I am trying to find out the complementary color of a given color using Python. here is my code. the code returns error message telling "AttributeError: 'list' object has no attribute 'join'" I need a hint. In addition, there  might be a more robust code which calculates the opposite/complementary color, which I am basically looking for. your suggestions will be helpful.</p>
  
  <pre><code>from PIL import Image  
  
  def complementaryColor(hex):
      """Returns complementary RGB color
  
      Example:
      &gt;&gt;&gt;complementaryColor('FFFFFF')
      '000000'
      """
      if hex[0] == '#':
          hex = hex[1:]
      rgb = (hex[0:2], hex[2:4], hex[4:6])
      comp = ['02%X' % (255 - int(a, 16)) for a in rgb]
      return comp.join()
  </code></pre>
  
  <p><strong><em>another similar function</em></strong></p>
  
  <pre><code>def blackwhite(my_hex):
      """Returns complementary RGB color
  
      Example:
      &gt;&gt;&gt;complementaryColor('FFFFFF')
      '000000'
      """
      if my_hex[0] == '#':
          my_hex = my_hex[1:]
      rgb = (my_hex[0:2], my_hex[2:4], my_hex[4:6])
      comp = ['%X' % (0 if (15 - int(a, 16)) &lt;= 7 else 15) for a in rgb]
      return ''.join(comp)
  
  
  print blackwhite('#36190D')
  </code></pre>