Mahapps Custom title bar color
You can set the title brush to whatever you want by setting WindowTitleBrush="Chocolate"
<Controls:MetroWindow x:Class="MetroDemo.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:MetroDemo="clr-namespace:MetroDemo" Title="MahApps.Metro - Demo Application" WindowTitleBrush="Chocolate"></Controls:MetroWindow>Hope this helps!