I'm creating a Windows Phone (7.5) app where I have the need to change some styles based on which Theme (Dark or Light) is selected.

It's not good enough for this app just to try and find a color which works in both cases.

Some of this can be done in code I know, but I would like to put it in xaml, as this is really just markup/styling which I don't want in my C# code :)

Here's what I would like to do in pseudo code:

```
    <ImageBrush x:Key="BackgroundImageBrush" ApplyForTheme="Dark" Stretch="None" 
ImageSource="/WindowsFanDkApp;component/Content/AppBackground.jpg"/>

    <ImageBrush x:Key="BackgroundImageBrush" ApplyForTheme="Light" Stretch="None" 
ImageSource="/WindowsFanDkApp;component/Content/AnotherAppBackground.jpg"/>

```

Can't seem to find any resources about how to do this...so I'm afraid it's not possible :(