Checkbox looks faded when selected

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WPF

Hi All,

I have a rather peculiar problem.
I have a CheckBox within a UserControl. Its unchecked by default.
When checked, the stroke (or tick) looks faded or washed out.

The following is the xaml code for the checkbox.

<StackPanel>
     <CheckBox Content="xyz" Name ="Check1"/>
     <CheckBox Margin="5" Content="SomeContent" Name="Check2" Click="OnClicked"/>
</StackPanel>

The following is the backend code:

void OnClicked(object sender, RoutedEventArgs e)
{
   // I intend to eventually filter a DataGrid when clicked on the check box
   CheckBox ck = sender as CheckBox;
   if(ck.IsChecked == true)
   {
      // Set some variable to true
   }
   else
   {
      // Set some variable to false
   }
   FilterGrid();  
}
void FilterGrid()
{
   // Apply filters to the DataGrid view collection
}

I initially thought that the method FilterGrid might be causing some kinda lag, but it does not.

Please help me out on this.

Thanks in advance.