This would be an option, but it's not very practical and wouldn't work in older browsers:
body:after {
content: "";
position: fixed;
top: 0; bottom: 0; left: 0; right: 0;
background: rgba(0,0,0,0.1);
pointer-events: none;
}
Or for even better color control, try hsla()
colors:
body:after {
content: "";
position: fixed;
top: 0; bottom: 0; left: 0; right: 0;
background: hsla(180,0%,50%,0.25);
pointer-events: none;
}
Really, it's better to play with the image in a image editor until you get the browser result you want.