that is what i do
.navbar-inverse .navbar-inner {
background-color: #E27403; /* it's flat*/
background-image: none;
}
.navbar-inverse .navbar-inner {
background-image: -ms-linear-gradient(top, #E27403, #E49037);
background-image: -webkit-linear-gradient(top, #E27403, #E49037);
background-image: linear-gradient(to bottom, #E27403, #E49037);
}
it works well for all navigator you can see demo here http://caverne.fr on the top