Change the color of the upward arrow on an open dropdown-menu

Update for Bootstrap 4.4 (year 2020): Use

<style>
.navbar .dropdown-toggle::after{ color:red; }
</style>

The arrow code can be found on line:2690 of the bootstrap.css. You can manipulate its position and color by modifying its css, e.g.:

.navbar .dropdown-menu:after {
  content: '';
  display: inline-block;
  border-left: 6px solid transparent;
  border-right: 6px solid transparent;
  border-bottom: 6px solid #000; /* change color here, modified for a black arrow */
  position: absolute;
  top: -6px;
  left: 10px;
}

In the latest Version of Bootstrap (v2.3.1), this has changed. It's now on line 694

.navbar .nav>li>.dropdown-menu:after{
content:'';
display:inline-block;
border-left:6px solid transparent;
border-right:6px solid transparent;
border-bottom:6px solid #ffffff;
position:absolute;
top:-6px
;left:10px;
}