Cross-Browser RGBa

RGBa-IE6-7.css

/* IE 7 and below: RGBa value in hex: aaRRGGBB */
* {
    background:transparent;
    zoom: 1;
    filter:progid:DXImageTransform.Microsoft.gradient(startColorstr=#7FC8C8C8,endColorstr=#7FC8C8C8);
}

RGBa-IE8.css

/* IE8: RGBa value in hex: aaRRGGBB */
* {
    background:transparent;
    -ms-filter:"progid:DXImageTransform.Microsoft.gradient(startColorstr=#7FC8C8C8,endColorstr=#7FC8C8C8)";
}

RGBa.css

* {
    /* Solid color fallback for no-RGBa support */
    background: rgb(200, 200, 200);
    /* RGBa declaration */
    background: rgba(200, 200, 200, 0.5);
}