WPF-Demo/WaaaghTheme.Resource/LightTheme.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <SolidColorBrush x:Key="BackgroundBrush" Color="LightPink"/>
    <SolidColorBrush x:Key="ForegroundBrush" Color="Coral"/>
</ResourceDictionary>