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Why is this WPF Button background not changing behind an image?

My squares are either SaddleBrown or WhiteSmoke in color, shifting to DarkTurquoise when selected. This works when there is no image on top of the squares. When I have a (PNG) image on top of the square the original SaddleBrown/WhiteSmoke color shows behind it but when the color is supposed to change to DarkTurquoise nothing happens to the background color of the square.
What could be the problem?
<ItemsControl.ItemTemplate>
<DataTemplate>
<Button x:Name="Square"
Command="{Binding DataContext.BoardGUI.SquareClickCommand, RelativeSource={RelativeSource AncestorType=ItemsControl}}"
CommandParameter="{Binding}">
<Button.Template>
<ControlTemplate TargetType="Button">
<Grid Background="{TemplateBinding Background}">
<Image Source="{Binding Source, Converter={StaticResource NullImageConverter}}"/>
</Grid>
</ControlTemplate>
</Button.Template>
</Button>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding SquareColor}" Value="Dark">
<Setter TargetName="Square" Property="Background" Value="SaddleBrown"/>
</DataTrigger>
<DataTrigger Binding="{Binding SquareColor}" Value="White">
<Setter TargetName="Square" Property="Background" Value="WhiteSmoke"/>
</DataTrigger>
<DataTrigger Binding="{Binding IsSelected}" Value="True">
<Setter TargetName="Square" Property="Background" Value="DarkTurquoise"/>
</DataTrigger>
</DataTemplate.Triggers>
</DataTemplate>
</ItemsControl.ItemTemplate>

As determined in the comments, based on the screenshot and the definition of the triggers, it appears that "SquareColor" is likely getting set or changed after IsSelected is set.

How to toggle image based on BooleanToVisibilityConverter?

In a WPF DataGrid, I have a DataGridTemplateColumn:
<DataGridTemplateColumn>
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<Image Visibility="{Binding ShowImage, Mode=OneWay, Convert{StaticResource BooleanToVisibilityConverter}}" Source="{StaticResource Image1}" />
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
This column starts with no image. Then some processing occurs. If ShowImage is assigned true, an image is displayed. Else, nothing is displayed.
How do I toggle between two images based on the assignment to ShowImage?

Just use another converter (maybe you can call it BoolToImageCoverter) that will assign one image if ShowImage is true and a different image if ShowImage is false.

You could use another converter, or you could use Style.Triggers:
<Image Source="{StaticResource Image1}">
<Image.Style>
<Style TargetType="{x:Type Image}">
<Setter Property="Visibility" Value="Collapsed" />
<Style.Triggers>
<DataTrigger Binding="{Binding ShowImage}" Value="True">
<Setter Property="Visibility" Value="Visible" />
</DataTrigger>
</Style.Triggers>
</Style>
</Image.Style>
</Image>

ListBox Loading Animation

I have a list box that should be filed when user click on Button,
sometimes the data loaded is quickly, and sometimes it take some time... Is there a simple way to load some animation like a clock, or something which can give the user indication that the process is running?
I use mvvm with button commands
<ListBox Width="30"
Visibility="{Binding IsDataLoaded,
Converter= {StaticResource BooleanToVisibilityConverter}}"
ItemsSource="{Binding Collection}"
FontSize ="15"
ScrollViewer.HorizontalScrollBarVisibility="Disabled" >
<ListBox.ItemContainerStyle>
<Style TargetType="ListBoxItem">
<Setter Property="IsEnabled" Value="False"/>
<Style.Triggers>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Foreground" Value="DarkGray" />
</Trigger>
</Style.Triggers>
</Style>
</ListBox.ItemContainerStyle>
</ListBox>
<Button Content="Go" Command="{Binding GoCommand}" IsEnabled="{Binding IsGoEnabled}" IsDefault="True" Width="60"
/>

Sounds like you're looking for a BusyIndicator like in the Extended Toolkit.

WPF ListBoxItem IsMouseOver

I have a ListBox, which on mousing over an item shows a delete button for that item. The problem is that the IsMouseOver triggers about 4 pixels into the highlighted item, so when mousing over multiple items, instead of the delete button seeming to move up and down with you, it flickers in the gaps between the items. Is there anyway to make IsMouseOver respond to the whole item?
<ListBox Name="lstLength" ItemsSource="{Binding Source={StaticResource lengths}}">
<ListBox.ItemTemplate>
<DataTemplate>
<DockPanel LastChildFill="True" Height="22">
<Button DockPanel.Dock="Right" Name="btnDelete" Content="X" Tag="{Binding}" Click="DeleteLength" Visibility="Collapsed" />
<TextBlock Text="{Binding}" />
</DockPanel>
<DataTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter TargetName="btnDelete" Property="Visibility" Value="Visible" />
</Trigger>
</DataTemplate.Triggers>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>

Each one of your items will be contained within a ListBoxItem, this is what gives the ~4 pixels between each item. It also provides the highlight and selection styling. You can style the listBoxItem via the ListBox.ItemContainerStyle property. Move your trigger to the item container and it should work as desired.

You could use a DataTrigger directly on the button (or try to apply the same RelativeSource binding in the place it is):
<Style TargetType="{x:Type Button}">
<DataTrigger Binding="{Binding IsMouseOver, RelativeSource={RelativeSource AncestorType=ListBoxItem}}"
Value="True">
<!-- ... -->
</DataTrigger>
</Style>

Adding Popup Border Animation around TextBox in C# wpf

I am currently developing a WPF application. When the user submits the form I have a method which checks to ensure that the fields are filled in and what I want to do is, if they are not, display a red to white gradient going around the box as a fade in animation.
Is this possible?

Use validation in your binding, and then assign a validation error template to the TextBox. Here's one that does a red rectangle:
<ControlTemplate x:Key="errorTemplate">
<Canvas Width="{Binding Path=AdornedElement.ActualWidth, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Adorner}}}"
Height="{Binding Path=AdornedElement.ActualHeight, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Adorner}}}">
<Border BorderBrush="Red" BorderThickness="1" >
<AdornedElementPlaceholder/>
</Border>
</Canvas>
</ControlTemplate>
Add this to the binding: Validation.ErrorTemplate="{StaticResource errorTemplate}

You can use a style and use data trigger to achieve this. This way, when your textbox is empty, you will see a red border and light red background. See the sample code below:
<Style x:Key="RequiredField" TargetType="{x:Type TextBox}">
<Style.Triggers>
<DataTrigger Binding="{Binding RelativeSource={RelativeSource Self}, Path=Text}" Value="">
<Setter Property="TextBox.BorderBrush" Value="{StaticResource MySolidBrush}" />
<Setter Property="TextBox.Background" Value="{StaticResource MyInnerBrush}"/>
<Setter Property="TextBox.ToolTip" Value="This Field is Mandatory"/>
</DataTrigger>
</Style.Triggers>
</Style>