CSS

how to have a background image with a color overlay

/* Working method */
.tinted-image {
  background: 
    /* top, transparent red, faked with gradient */ 
    linear-gradient(
      rgba(255, 0, 0, 0.45), 
      rgba(255, 0, 0, 0.45)
    ),
    /* bottom, image */
    url(image.jpg);
}

html background image with color overlay "hsl"

#header {
  background: url("img/image.jpg") 0 0 no-repeat fixed;
  height: 100%;
  overflow: hidden;
  background-color: hsl(206, 27%, 38%);
  background-blend-mode: multiply;
}

overlay color on image css

footer#site-footer{  
  position:relative;
}

footer#site-footer:before {     /* use before property (pseudo-element)  */
    position: absolute;
    content: '';
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0,0,0,0.3);
}