CodePen

HTML

            
              (an old school calculator word game ;)
<h1 class="hex">hello</h1>

<br>
<pre>
filter:progid:DXImageTransform.Microsoft.gradient(startColorstr=<span class="hex"></span>,endColorstr=<span class="hex"></span>);
</pre>

<p>See: http://css-tricks.com/rgba-browser-support/</p>
            
          
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CSS

            
              
            
          
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JS

            
              function ieRGBA(rr, gg, bb, aa) {
  'use strict';
  /*
    @rr, @gg, @bb (Integer) Color value - 0 to 255
    @aa (Float) Opacity - 0 to 1 eg. 0.5
    
    returns: #AARRGGBB (Hex String)
  */
  return '#' + [
    parseInt(aa * 255, 10).toString(16),
    ('00' + (rr).toString(16)).slice(-2),
    ('00' + (gg).toString(16)).slice(-2),
    ('00' + (bb).toString(16)).slice(-2)
  ].join('').toUpperCase();
}

var rgba = ieRGBA(11, 115, 85, 0.6925),
    hex = document.getElementsByClassName('hex');

hex[0].innerHTML = rgba;
hex[1].innerHTML = rgba;
hex[2].innerHTML = rgba;

            
          
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