title: glClearColor(0, 0, 0, 0) is transparent, not black
body: <p>I'm trying to use OpenGL my first time. I was looking at some code online and then tried to write my own, but I always just got an empty (transparent) window. (I used GLUT to open the window).</p>
  
  <p>I thought I did something wrong, so I copyied the code from <a href="http://www.mario-konrad.ch/wiki/lib/exe/fetch.php?media=programming:opengl:tutorial-01:tutorial01.cpp" rel="nofollow noreferrer">here</a> to my C source-code, and my window is still transparent. Also, the <em>alpha</em> parameter for <em>glClearColor()</em> does not seem to have any effect. Instead, the alpha-value <strong>seems</strong> to be determined by the <em>red</em>, <em>green</em> and <em>blue</em> parameters.</p>
  
  <p><code>glClearColor(0, 0, 0, 0)</code><br>
  <code>glClearColor(0, 0, 0, 1)</code><br>
  <img src="https://i.stack.imgur.com/ijeYJ.jpg" alt="enter image description here"></p>
  
  <p><code>glClearColor(1, 0, 0, 0)</code><br>
  <code>glClearColor(1, 0, 0, 1)</code><br>
  <img src="https://i.stack.imgur.com/F9Wr6.jpg" alt="enter image description here"></p>
  
  <p><code>glClearColor(1, 1, 0, 0)</code><br>
  <code>glClearColor(1, 1, 0, 1)</code><br>
  <img src="https://i.stack.imgur.com/R4YLq.jpg" alt="enter image description here"></p>
  
  <p><code>glClearColor(1, 0, 0, 0)</code><br>
  <code>glClearColor(1, 0, 0, 1)</code><br>
  <img src="https://i.stack.imgur.com/RQKH4.jpg" alt="enter image description here"></p>
  
  <p>The <em>alpha</em> parameter doesn't change the result.</p>
  
  <p>I use Ubuntu 12.04 LTS, <em>libgl1-mesa-dev</em>.</p>
  
  <p>Is this a bug or do I do something wrong?</p>