CSS Validation

Hello,

After I used the CSS Validator I got an error report,
which stated :

property opacity does not exist : 0.85

and subsequently the property was erased in the "validated stylesheet"

As I checked the w3.org,
I found that "opacity" is a valid property
(http://www.w3.org/TR/css3-color/#opacity)

Now who's right ?

Kind regards

W.Van den Eynde