CSS
.contenido{
background-color: #FFFFFF;
text-align: justify;
margin:auto;
margin:10px;
padding:14px;
width:500px;
}
.colorsito {
background: #000000;
width:400px;
opacity: 1;
float:left;
padding:10px;
margin:10px;
z-index:900;
position:absolute;
-webkit-transition: all .7s ease-in;
-moz-transition: all .7s ease-in;
-o-transition: all .7s ease-in;
}

.contenido:hover .colorsito {
opacity: 0;
-webkit-transition: all .9s ease;
-moz-transition: all .9s ease;
-o-transition: all .9s ease;
}


Capas

<div class="contenido"><Div class="colorsito">

Aqui lo que quiera que desaparesca

</div></div>