Issue with webkit tap highlight color not being applied

Question

I'm having trouble to get the -webkit-tap-highlight-color property to apply to a div - I'm at a loss as to why it isn't. Copying all the styles that apply to it below. The desired outcome is a back button as shown here: http://building-iphone-apps.labs.oreilly.com/ch03.html#ch03_id35932102

.backButton {
  font-weight: bold;
  text-align: center;
  line-height: 28px;
  color: white;
  text-shadow: rgba(0,0,0,0.6) 0px -1px 0px;
  position: absolute;
  top: 13px;
  left: 6px;
  font-size: 14px;
  max-width: 50px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  border-width: 0 8px 0 14px;
  -webkit-tap-highlight-color:rgba(0,0,0,0);
  -webkit-border-image: url(/static/images/backButton.png) 0 8 0 14;
}
.backButton.clicked {
  -webkit-border-image: url(/static/images/back_button_clicked.png) 0 8 0 14;
}

.toolbar{ 
  background-color: #e1f7ff; 
  -webkit-box-sizing:border-box; 
  border-bottom:1px solid #559D75; 
  padding:10px; 
  height:53px; 
  background-image:-webkit-gradient(linear,left top,left bottom,from(#e1f7ff),to(#a1d2ed)); 
  position:relative; 
  z-index: 70; }

Applied here:

<div class='toolbar'>
    <div class='backButton'>Back</div>
</div>

Viewing it in iPhone simulator (OS 4 enabled) and Safari - same problem with both (tap highlight still shows up).

Thanks in advance.