How do I match my controls' styles to the current theme? (WPF)

If I create a custom control with WPF, how can I provide styles for the control that match the currently applied theme (Aero, Luna, Classic, etc.)?

For example I'd like to apply the following when using Aero:

<Style>
    <Setter Property="Background" Value="White"/>
</Style>

But then apply a different style when using Luna:

<Style>
    <Setter Property="Background" Value="#DFDFDF"/>
</Style>

Can I somehow extend the base themes to provide support for my new control?