background-color opacity declaration

[lionelts]

When i change in topstyle css file
background-color: rgba(102, 102, 102, 1);
by
background-color: #666666 ;
opacity: 1;
it is ok in the topstyle preview IE 10 .

In all he case it is ok in IE 10 browser !!!
it is strange that the same IE rendering engine don't show the same thing in topstyle IE preview !! ?

regard's
http://www.css3.info/introduction-opacity-rgba/