title: What are differences between RGB vs RGBA other than 'opacity'
body: <p>I have moved beyond using standard colors in CSS by declaring them <code>orange</code>, <code>blue</code>, <code>aquamarine</code>, etc..., and have been using <code>rgb()</code> like so for the same colors respectively, <code>rgb(255,165,0)</code>, <code>rgb(0,0,255)</code> and <code>rgb(127,255,212)</code> (thanks to the <a href="https://coderwall.com/p/a1qqiw">ColorHighlighter</a> package in ST3).</p>
  
  <p>Upon altering a gradient for bootstrap <code>.btn</code> I came across <code>rgba()</code>.  Quick research explains that <code>a</code> stands for <code>alpha</code>, and theres a whole bunch of integral math attributed to  <a href="http://en.wikipedia.org/wiki/Edwin_Catmull">Catmull</a> and <a href="http://en.wikipedia.org/wiki/Alvy_Ray_Smith">Smith</a>.  It is also somewhat easy to find that the alpha channel is used for "alpha compositing", which can mostly be associated as "opacity".</p>
  
  <ul>
  <li>Are there differences between the two other than opacity?  </li>
  <li>Why isn't it convention to use RGBA.(I'm assuming this since I am
  just now stumbling onto this)</li>
  <li>Are there other limitations that should be know when using rgba() for
  the web?</li>
  <li>Is there a shortcut to declare opacity beside a color shortcut? (ie
  <code>color: salmon:.5;</code>)</li>
  <li>From a web developer standpoint, do I need to worry about the
  differences between ARGB, RGBA, BGRA byte order for different
  machines <a href="http://en.wikipedia.org/wiki/RGBA">INFO</a>?</li>
  <li>Other important information?</li>
  </ul>