Yes, with CSS3
Using CSS3 gradient
calls to make "non-gradient" solid colors will give you multiple background colors with transparency capability. Here's two solid colors at 50% transparency overlaid (see a fiddle):
.layeredBkg {
background-image: -o-linear-gradient(left , rgba(46,227,255.5) 0%, rgba(46,227,255,.5) 100%), -o-linear-gradient(left , rgba(196,48,255.5) 0%, rgba(196,48,255,.5) 100%);
background-image: -moz-linear-gradient(left , rgba(46,227,255,.5) 0%, rgba(46,227,255,.5) 100%), -moz-linear-gradient(left , rgba(196,48,255,.5) 0%, rgba(196,48,255,.5) 100%);
background-image: -webkit-linear-gradient(left , rgba(46,227,255,.5) 0%, rgba(46,227,255,.5) 100%), -webkit-linear-gradient(left , rgba(196,48,255,.5) 0%, rgba(196,48,255,.5) 100%);
background-image: -webkit-gradient(linear,left top, right top, color-stop(0, rgba(46,227,255,.5)), color-stop(1, rgba(46,227,255,.5))), -webkit-gradient(linear,left top, right top, color-stop(0, rgba(196,48,255,.5)), color-stop(1, rgba(196,48,255,.5)));
background-image: -ms-linear-gradient(left , rgba(46,227,255,.5) 0%, rgba(46,227,255,.5) 100%), -ms-linear-gradient(left , rgba(196,48,255,.5) 0%, rgba(196,48,255,.5) 100%);
background-image: linear-gradient(left , rgba(46,227,255,.5) 0%, rgba(46,227,255,.5) 100%), linear-gradient(left , rgba(196,48,255,.5) 0%, rgba(196,48,255,.5) 100%);
filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#882ee3ff', endColorstr='#882ee3ff'), progid:DXImageTransform.Microsoft.gradient(startColorstr='#88c430ff', endColorstr='#88c430ff');
}