Alterar a cor e a opacidade dos placeholders no form via css

O Código:

::-webkit-input-placeholder { /* WebKit browsers */
    color: #999; opacity:1; filter:alpha(opacity=100);
}

:-moz-placeholder { /* Mozilla Firefox 4 to 18 */
    color: #999; opacity:1; filter:alpha(opacity=100);
}

::-moz-placeholder { /* Mozilla Firefox 19+ */
    color: #999; opacity:1; filter:alpha(opacity=100);
}
:-ms-input-placeholder { /* Internet Explorer 10+ */
    color: #999; opacity:1; filter:alpha(opacity=100);
}

hasta!