title: Color of setPixel
body: <p>Found an example:</p>
  
  <pre><code>raster.setPixel( pf, jj, clr );
  </code></pre>
  
  <p>But <em>clr</em> has 4 elements:</p>
  
  <pre><code>static int[] clr = {0, 0, 0, 255}; 
  </code></pre>
  
  <p>Why? What does that 4th element mean? It doesn't work without it, throws ArrayIndexOutOfBoundsException.</p>