If you want a dark background, use navbar-inverse instead of navbar-default.

<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Bootstrap Centered Navbar</title>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<!-- Latest compiled and minified Bootstrap CSS-->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
<style>
body {
font-family: Gotham, "Helvetica Neue", Helvetica, Arial, sans-serif;
background-color: #000;
color: #FFF;
}
h1 {font-weight: 500}
/**CSS for centered navigation**/
@media (min-width: 768px) {
.navbar-nav { float: none; }
.nav.navbar-nav {
display: flex;
justify-content: center;
flex-wrap: wrap;
}
}
</style>
</head>
<body>
<div class="container">
<header class="row">
<div class="col-xs-12">
<h1 class="text-center">Dominique Bello <em>Silk Art</em></h1>
</div>
</header>
<div class="row">
<!--begin top nav bar-->
<nav class="navbar navbar-inverse" role="navigation">
<div class="container-fluid">
<div class="navbar-header">
<button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#myNavbar">
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
</div>
<div class="collapse navbar-collapse" id="myNavbar">
<ul class="nav navbar-nav">
<li class="active"><a href="#">HOME</a></li>
<li class="dropdown"><a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Galleries<span class="caret"></span></a>
<ul class="dropdown-menu">
<li><a href="abayas.html">Abayas</a></li>
<li><a href="coats.html">Coats</a></li>
<li><a href="jackets.html">Jackets</a></li>
<li><a href="kimonos.html">Kimonos</a></li>
<li><a href="forthesakeofart.html">For the Sake of Art</a></li>
</ul>
</li>
<li ><a href="contact.html">Contact</a></li>
</ul>
</div>
</div>
</nav>
</div>
</div>
<!--Latest compiled & minified jQuery 3 JS-->
<script src="https://code.jquery.com/jquery-3.2.1.min.js" integrity="sha256-hwg4gsxgFZhOsEEamdOYGBf13FyQuiTwlAQgxVSNgt4=" crossorigin="anonymous"></script>
<!--Latest compiled & minifed Bootstrap JS-->
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
</body>
</html>