title: Drawing a solid sphere with transparency in openGL
body: <p>I want to draw a <code>glutSolidSphere</code> with some transparency, but it doesn't seem to work.</p>
  
  <pre><code>glColor4f(1, 0, 0, 0); // should be completely invisible
  glPushMatrix();
  glTranslatef(position.x, position.y, position.z);
  glutSolidSphere(3, 5, 5);
  glPopMatrix();
  </code></pre>
  
  <p>In my main function, I initialize with the following display mode:</p>
  
  <pre><code>glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA | GLUT_ALPHA);
  </code></pre>
  
  <p>What am I missing here?</p>