title: how to create a triangle filled in a translucent color by python pillow(fork PIL)
body: <pre><code>im = Image.new('RGB', (255, 255))
  draw = ImageDraw.Draw(im)
  draw.polygon([(0, 0), (0, 255), (255, 255), (255, 0)], fill = 'white')
  draw.polygon([(1,1), (20, 100), (100,20)], fill = (200, 0, 0)) # outline='red', fill='blue'
  im.save('my_pic.png')
  </code></pre>
  
  <p>I know how to create triangle and fill some RGB color in it.
  But I do not know how to fill rGBA color into it. (or other translucent color size)</p>
  
  <p>And on the other side ,if I can create first triangle with a translucent color ,when I draw second one, the second one can or can not mix the color with first triangle?</p>