The class is .navbar-default. You need to create a class on your custom css .navbar-default.And follow the css code. Also if you don’t want box-shadow on your menu, you can put on the same class.
.navbar-default {
background-color:transparent !important;
border-color:transparent;
background-image:none;
box-shadow:none;
}
To change font navbar color, the class is to change – .navbar-default .navbar-nav>li>a see the code bellow:
.navbar-default .navbar-nav>li>a {
font-size:20px;
color:#fff;
}
ref : http://twitterbootstrap.org/bootstrap-navbar-background-color-transparent/