title: R function for RGBA to HEX color conversion
body: <p>I am looking for some <a href="/questions/tagged/function" class="post-tag" title="show questions tagged &#39;function&#39;" rel="tag">function</a> in <a href="/questions/tagged/r" class="post-tag" title="show questions tagged &#39;r&#39;" rel="tag">r</a> which can convert a <a href="/questions/tagged/rgba" class="post-tag" title="show questions tagged &#39;rgba&#39;" rel="tag">rgba</a> color to Hex e.g. <code>rgba(240, 177, 76, 0.80)</code>. There are plethora of functions available from <a href="/questions/tagged/rgb" class="post-tag" title="show questions tagged &#39;rgb&#39;" rel="tag">rgb</a> to Hex conversion e.g. <code>plotrix::rgb.to.hex()</code> but not for RGBA.</p>
  
  <p>Really appreciate any pointer.</p>