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XAML: How to bind over 2 properties to a DynamicResourceExtension

I have a ResourceDictionary for Colors:
<ResourceDictionary>
<Color x:Key="Ori">#000000</Color>
</ResourceDictionary>
Then use DynamicResource to reference them:
<DynamicResource x:Key="Ref", ResourceKey="Ori" />
When over 2 properties bind to Ref:
<SomeControl1.Background>
<SolidColorBrush Color="{StaticResource Ref}">
</SomeControl1.Background>
<SomeControl2.Background>
<SolidColorBrush Color="{StaticResource Ref}">
</SomeControl2.Background>
It would cause when running:
"Ref" is not a valid value for property "Color"
I guess that's because they're both TwoWay Bindings.
Any method to fix?

You can simply do it in that way:
<ResourceDictionary>
<Color x:Key="Ori">#000000</Color>
</ResourceDictionary>
Your controls:
<SomeControl1.Background>
<SolidColorBrush Color="{DynamicResource Ori}">
</SomeControl1.Background>
<SomeControl2.Background>
<SolidColorBrush Color="{DynamicResource Ori}">
</SomeControl2.Background>
Using also StaticResource is weird.

Change slider bar color

It should be very easy to do this but I haven't found the information that I need. What I want is as simple as changing the color of the slider bar:
I'm using ModernUI and the default bar color is very similar to my background and I want to make it a bit lighter.

You should be able to change it editing the template.
Right click your Slider, Edit Template -> Edit Copy.;.
A new window will appear asking you where VS should put the XAML code for the ControlTemplate and Styles. Chek the tags and such.
Good luck!
Edit:
Ok, here it goes.
Assuming that you already have a ModernUI App, create a new folder called Assets, right click it Add -> New Item... -> ModernUI Theme. Call it whatever you like it.
Inside the newly created XAML file insert these SolidColorBrush under the AccentColor Color tag:
<SolidColorBrush x:Key="SliderSelectionBackground" Color="Red" />
<SolidColorBrush x:Key="SliderSelectionBorder" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBackground" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBackgroundDisabled" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBackgroundDragging" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBackgroundHover" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBorder" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBorderDisabled" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBorderDragging" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBorderHover" Color="Red" />
Each one of these represents a state of the Thumb (the slider "rectangle"). After that open your App.xaml file and include your theme there (this is what my file looks like):
<Application x:Class="ModernUIApp1.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
StartupUri="MainWindow.xaml">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/FirstFloor.ModernUI;component/Assets/ModernUI.xaml" />
<ResourceDictionary Source="/FirstFloor.ModernUI;component/Assets/ModernUI.Light.xaml"/>
<ResourceDictionary Source="/Assets/ModernUI.Theme1.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
The <ResourceDictionary Source="/Assets/ModernUI.Theme1.xaml" /> bit represents my theme.
Setting all the colors to Red, this is what it looked like:
I guess that's more clear!
Hope you like it.
EDIT:
It will change when you apply your theme. But, as you're familiar with styles, I'm sending the complete template. What you can do is create a UserDictionary with only this template and when you you want to use it, change the slider Template property. You'll want to change only the Thumb Tags. Pastebin code
And if you want to change only THIS one put the template between <Windows.Resources> or <Slider.Resources> - Another option would be create your own control

I found two approaches:
You can customize your slider by insert corresponding brushes in
appropriate Slider.Resources section.
You can add brushes to separate xaml file with dictionary and then
merge it with corresponding slider in the Slider.Resources. In some cases it fits better because you can change colors of few controls at once.
Any does not need to changing of the control's template.
Both approaches are presented below:
Page1.xaml
<Grid Style="{StaticResource ContentRoot}">
<StackPanel>
<!-- Slider with default theme and colors from ModernUI -->
<Slider/>
<!-- Slider with custom colors from approach 1 -->
<Slider>
<Slider.Resources>
<SolidColorBrush x:Key="SliderSelectionBackground" Color="Green" />
<SolidColorBrush x:Key="SliderSelectionBorder" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBackground" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBackgroundDisabled" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBackgroundDragging" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBackgroundHover" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBorder" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBorderDisabled" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBorderDragging" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBorderHover" Color="Green" />
</Slider.Resources>
</Slider>
<!-- Slider with custom colors from approach 2 -->
<Slider>
<Slider.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Dictionary1.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Slider.Resources>
</Slider>
</StackPanel>
</Grid>
Dictionary1.xaml
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<SolidColorBrush x:Key="SliderSelectionBackground" Color="Blue" />
<SolidColorBrush x:Key="SliderSelectionBorder" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBackground" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBackgroundDisabled" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBackgroundDragging" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBackgroundHover" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBorder" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBorderDisabled" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBorderDragging" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBorderHover" Color="Blue" />
</ResourceDictionary>
As result you get following:

Foreground property is used to fill the "completed" part of the slider with a particular color. (Background does the uncompleted part.)
<Slider Value="40" Maximum="100" Foreground="Red" />

Here you have the templates you should use: Slider Styles and Templates
The property you are looking to edit is the TrackBackground.BackGround.
If you define a style for this control template and put it either in you app.xaml or in the window.resources or in any other file, as long as you give it a key you can use it in a specific slider through the "Style" property of that slider using that same key.

Windows 8.1 Store/Phone Apps.
Add this to the App.xaml and change the color values to your liking:
<ResourceDictionary>
<ResourceDictionary.ThemeDictionaries>
<ResourceDictionary x:Key="Default">
<SolidColorBrush x:Key="SliderTrackDecreaseBackgroundThemeBrush" Color="#FFFF0000" />
<SolidColorBrush x:Key="SliderTrackDecreasePointerOverBackgroundThemeBrush" Color="#FF00FF00" />
<SolidColorBrush x:Key="SliderTrackDecreasePressedBackgroundThemeBrush" Color="#FF0000FF" />
</ResourceDictionary>
<ResourceDictionary x:Key="Light">
</ResourceDictionary>
<ResourceDictionary x:Key="HighContrastBlack">
</ResourceDictionary>
<ResourceDictionary x:Key="HighContrastWhite">
</ResourceDictionary>
</ResourceDictionary.ThemeDictionaries>
</ResourceDictionary>
You probably only want to change the slider for the default theme and probably only the three color values shown above. For all colors / resources that you can change, see this link at MSDN: Slider styles and templates.

For what it's worth, the only way I could change the Slider Thumb color on Win10 UWP for Phone was to overwrite the System Foreground brush. (You can also apparently completely re-template the whole Slider)
So, I put into my App.xaml
<Application
x:Class="App1.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:App1"
RequestedTheme="Dark">
<Application.Resources>
<SolidColorBrush x:Key="SystemControlForegroundAccentBrush" Color="White" />
</Application.Resources>
</Application>
The addition to Application.Resources is the really important thing here. It's where we're overwriting the Foreground color for ALL common elements, like Checkbox, ContentDialog, ProgressRing, etc.... So, that's the downside to this method too.
Changing the Thumb color on a Slider is a known problem point for XAML UWP. Microsoft has plans to make it easier in the immediate future.

Style of MediaElement in Windows 8.1

How can I change style of sample MediaElement:
For example how can I change the background.
Code:
<MediaElement AudioCategory="BackgroundCapableMedia" x:Name="media" MediaEnded="Media_MediaEnded" AutoPlay="True" AreTransportControlsEnabled="True" IsMuted="False" Volume="0.5"/>

Actually you can change the colors by overriding the default colors in the App. Note this would apply now for all MediaElement controls with transport controls, but it is possible. In your App.xaml you would provide overrides for these values like this:
<Application.Resources>
<SolidColorBrush x:Key="MediaButtonForegroundThemeBrush" Color="Blue" />
<SolidColorBrush x:Key="MediaButtonBackgroundThemeBrush" Color="Transparent" />
<SolidColorBrush x:Key="MediaButtonPointerOverForegroundThemeBrush" Color="#FFFFFFFF" />
<SolidColorBrush x:Key="MediaButtonPointerOverBackgroundThemeBrush" Color="#26FFFFFF" />
<SolidColorBrush x:Key="MediaButtonPressedForegroundThemeBrush" Color="#FF000000" />
<SolidColorBrush x:Key="MediaButtonPressedBackgroundThemeBrush" Color="#FFFFFFFF" />
<SolidColorBrush x:Key="MediaButtonPressedBorderThemeBrush" Color="#FFFFFFFF" />
<SolidColorBrush x:Key="MediaControlPanelVideoThemeBrush" Color="Red" />
<SolidColorBrush x:Key="MediaControlPanelAudioThemeBrush" Color="#FF000000" />
<SolidColorBrush x:Key="MediaDownloadProgressIndicatorThemeBrush" Color="#38FFFFFF" />
<SolidColorBrush x:Key="MediaErrorBackgroundThemeBrush" Color="#FF000000" />
<SolidColorBrush x:Key="MediaTextThemeBrush" Color="#FFFFFFFF" />
</Application.Resources>
This would give you a visual like this:
Hope this helps!

I think if you do not want to write your own controlpanel with play-pause-stop controls, you can not change the background of this MediaElement rendered controlpanel because it is an overlay of the video and is designed to look MS/Windows8 conform.
Note: This controlpanel is also invisible if you do not mouse-over the video.

Change selection highlight color in list view

How do I do this? Everything I've founds says this should work, but it doesn't for me. What am I doing wrong?
<ListView ItemsSource="{Binding ListViewItems}" >
<ListView.ItemContainerStyle>
<Style TargetType="ListBoxItem">
<Style.Resources>
<SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="Green"/>
</Style.Resources>
</Style>
</ListView.ItemContainerStyle>
</ListView>

The code you have shown above does work for me. This, however, sets the colors when ListBox is in focus. To set the color when it is not in focus, try ...
<SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}" Color="Green" />
Check this example to implement it on Win 8.

Try to directly set it in <ListView.Resources><SolidColorBrush x:Key=...></ListView.Resources>
Try to define a SolidColorBrush with Key "{x:Static SystemColors.InactiveSelectionHighlightBrushKey}" too.
UPDATE:
Just tried to run the following xaml on win7 and targeting .net 4.5:
<ListView ItemsSource="{Binding DummyItems}">
<ListView.Resources>
<SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="Green"/>
<SolidColorBrush x:Key="{x:Static SystemColors.InactiveSelectionHighlightBrushKey}" Color="LightGreen"/>
</ListView.Resources>
</ListView>
Works like a charm!
Nevertheless, it seems to be that this is not going to work on win8.
So there may be no way of getting around to define your own template. Refer to this page.

Custom GridViewItem Selection - Windows Store App C#/XAML

I'm trying to change the style of selecting items in a gridview. Below the code I'm using in StandardStyles.xaml:
<SolidColorBrush x:Key="ListViewItemSelectedBackgroundThemeBrush" Color="Transparent"/>
<SolidColorBrush x:Key="ListViewItemPointerOverBackgroundThemeBrush" Opacity="0.25" Color="Blue"/>
<SolidColorBrush x:Key="ListViewItemSelectedPointerOverBackgroundThemeBrush" Opacity="0.7" Color="Blue"></SolidColorBrush>
<SolidColorBrush x:Key="ListViewItemSelectedPointerOverBorderThemeBrush" Color="Blue"/>
But I need what the border with the selected icon stay with some style and the background transparent, like this:
Selected Image Style
Could someone help me?

When I use a rectangle in StandardStyles.xaml beneath each GridViewItem the custom selection works.
<DataTemplate x:Key="MyTemplete">
<Grid HorizontalAlignment="Left" Background="Transparent">
<Rectangle>
<Rectangle.Fill>
<SolidColorBrush Color="White" Opacity="1"/>
</Rectangle.Fill>
</Rectangle>
...
</Grid>
</DataTemplate>

Use the code below to set the style of a selected item. It will set the border color, the text color and the check icon color.
<SolidColorBrush x:Key="ListViewItemSelectedBackgroundThemeBrush" Color="#323232"></SolidColorBrush>
<SolidColorBrush x:Key="ListViewItemSelectedForegroundThemeBrush" Color="White"></SolidColorBrush>
<SolidColorBrush x:Key="ListViewItemCheckThemeBrush" Color="White"></SolidColorBrush>
Regards.