Is it possible to change only the alpha of a rgba background colour on hover?

Question

I have a set of tags with differing rgba background colours but the same alpha. Is it possible to write a single css style that will change only the o

Answer 1

I had a similar problem. I had 18 different divs working as buttons, and each with a different color. Rather than figure out the color codes for each or use a div:hover selector to change the opacity (which affects all children) I used the pseudo-class :before like in @Chris Boon's answer.

Because I wanted to do the coloring on the individual elements, I used :before to create a transparent white div on :hover. This is a very basic washout.

#categories div {
    position:relative;
    width:100px;
    height:100px;
    float:left;
    border:1px solid black;
    display:table-cell;
}

#categories div:before{
    content:"";
    position:absolute;
    top:0px;
    left:0px;
    width:100px;
    height:100px;
}

#categories div:hover:before {
    background-color:white;
    opacity:0.2;
}

#a_Particular_Div {
    background-color:red;
}

According to CanIUse.com, this should have something like 92% support as of early 2014. (http://caniuse.com/#feat=css-gencontent)