override theme resource 'DataGridColumnHeaderBackgroundBrush' for DataGridColumnHeader in UWP doesn't work in 5.1.0 version

[xiedongweo]

I'm submitting a...

Bug report (I searched for similar issues and did not find one)

Current behavior

I want to change the default DataGridColumnHeader's background color. I use the following code on XAML page:

<Page.Resources> <SolidColorBrush x:Key="DataGridColumnHeaderBackgroundBrush" Color="Blue"/> </Page.Resources>

I'm using the nuget package 5.1.0(https://www.nuget.org/packages/Microsoft.Toolkit.Uwp.UI.Controls.DataGrid/5.1.0)

With this package, the DataGridColumnHeader's background color did get changed.

But I found that if I back to use Package 5.0.0 (https://www.nuget.org/packages/Microsoft.Toolkit.Uwp.UI.Controls.DataGrid/5.0.0)

It will work.

Expected behavior

The DataGridColumnHeader's background color should change to blue.

Minimal reproduction of the problem with instructions

`<Page.Resources>
    <SolidColorBrush x:Key="DataGridColumnHeaderBackgroundBrush" Color="Blue"/>
</Page.Resources>
<Grid>
    <controls:DataGrid x:Name="EmployeeGrid"
              ItemsSource="{x:Bind Persons}"
              AutoGenerateColumns="False">
        <controls:DataGrid.Columns>
            <controls:DataGridTextColumn Header="First Name"
                                         Binding="{Binding FirstName}"/>
            <controls:DataGridTextColumn Header="Last Name"
                                         Binding="{Binding LastName}"/>
            <controls:DataGridTextColumn Header="Position"
                                         Binding="{Binding Position}"/>
            <controls:DataGridComboBoxColumn Header="Department"
                                             Binding="{Binding DepartmentId}"                                                  
                                             ItemsSource="{x:Bind Departments, Mode=OneWay}"
                                             DisplayMemberPath="DepartmentName"/>
        </controls:DataGrid.Columns>
    </controls:DataGrid>
</Grid>`

`public sealed partial class MainPage : Page
{
    public List<Department> Departments { get; set; }
    public List<Person> Persons { get; set; }
    public MainPage()
    {
        this.InitializeComponent();
        Departments = new List<Department>
    {
        new Department {DepartmentId = 1, DepartmentName = "R&D"},
        new Department {DepartmentId = 2, DepartmentName = "Finance"},
        new Department {DepartmentId = 3, DepartmentName = "IT"}
    };

        Persons = new List<Person>
    {
        new Person
        {
            PersonId = 1, DepartmentId = 3, FirstName = "Ronald", LastName = "Rumple",
            Position = "Network Administrator"
        },
        new Person
        {
            PersonId = 2, DepartmentId = 1, FirstName = "Brett", LastName = "Banner",
            Position = "Software Developer"
        },
        new Person
        {
            PersonId = 3, DepartmentId = 2, FirstName = "Alice", LastName = "Anderson",
            Position = "Accountant"
        }
    };
    }

    
}

public class Department
{
    public int DepartmentId { get; set; }
    public string DepartmentName { get; set; }
}

public class Person
{
    public int PersonId { get; set; }
    public int DepartmentId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Position { get; set; }
}`

Environment

Nuget Package(s): https://www.nuget.org/packages/Microsoft.Toolkit.Uwp.UI.Controls.DataGrid/5.1.0

Package Version(s): 5.1.0

Windows 10 Build Number: 
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] Insider Build (build number: )
- [x] May 2019 Update 18362

App min and target version:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [x ] October 2018 Update (17763)
- [ ] Insider Build (xxxxx)

Device form factor:
- [x] Desktop
- [ ] Mobile
- [ ] Xbox
- [ ] Surface Hub
- [ ] IoT

Visual Studio 
- [ ] 2017 (version: )
- [ ] 2017 Preview (version: )
- [x] 2019 (16.1.0)

[RBrid]

This must be because of some of Daniel's four changes in DataGrid.xaml:
f22ce48 Daniel Martín González 1/9/2019 7:49:31 AM +00:00 Change DataGridColumnHeaderBackgroundBrush to SystemAltHighColor
3ad0e2e Daniel Martin Gonzalez 1/3/2019 3:50:44 PM +00:00 Merge branch 'master' into datagrid#2373
ca87b5f Daniel Martín González 10/4/2018 8:46:01 PM +00:00 Fix SolidColorBrush to Color
54079a6 Daniel Martín González 10/3/2018 6:36:25 PM +00:00 Fix DataGrid colours not adapting to Dark Theme

I was able to get it working by using:

  <Page.Resources>
    <Color x:Key="MyColumnHeaderBackgroundColor">#C4AF8D</Color>
    <StaticResource x:Key="DataGridColumnHeaderBackgroundColor" ResourceKey="MyColumnHeaderBackgroundColor"/>
  </Page.Resources>

Hope that works for you. Thanks.