How to change Navigation Bar Color

Here is my code:

public partial class MainPage : MasterDetailPage
{
        public MainPage()
        {
                Detail = new NavigationPage(new RootPage());
        }
}

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage Title="Root" xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="my.RootPage">
    <ContentPage.ToolbarItems>
        <ToolbarItem   Name="Refresh" Icon="" Activated="OnRefresh" />
    </ContentPage.ToolbarItems>

    <ContentPage.Content >
        <StackLayout >
            ...
        </StackLayout>
    </ContentPage.Content>
</ContentPage>

How do i change so that I can change the Page's background color including the Toolbar as well?