You can implement a "style selector" by using different style XMLs.
Just define a theme named "StyleSelector" or something like that in /res/**values**/styles.xml
:
<?xml version="1.0" encoding="utf-8"?>
<resources>
<style name="ThemeSelector" parent="@android:style/Theme.Black">
... Your theme definitions
</style>
</resources>
Then create a /res/**values-v11**/styles.xml
:
<resources>
<style name="ThemeSelector" parent="@android:style/Theme.Holo">
</style>
</resources>
Now just apply your theme with "@style/ThemeSelector
" and let Android do the magic.
On older Android versions, your theme definition will be loaded, on newer versions with Holo-Support, your theme will be derived from Holo.