I want a color overlay on this header element. How can I do this with CSS?
You should use rgba for overlaying your element with photos.rgba is a way to declare a color in CSS that includes alpha transparency support. you can use .row as an overlayer like this:
#header {
background: url(../img/bg.jpg) 0 0 no-repeat fixed;
height: 100%;
overflow: hidden;
color: #FFFFFF
}
.row{
background: rgba(39,62,84,0.82);
overflow: hidden;
height: 100%;
z-index: 2;
}