To get a ProgressBar in the default theme that is to be used on white/light back ground, use one of the inverse styles:
<ProgressBar style="@android:style/Widget.ProgressBar.Inverse"/>
<ProgressBar style="@android:style/Widget.ProgressBar.Large.Inverse"/>
<ProgressBar style="@android:style/Widget.ProgressBar.Small.Inverse"/>
This will usually give you a black on transparent ProgressBar, but some OS installs use custom assets. If you're looking for a specific color, you'll have to roll your own drawables by following the instructions provided by CommonsWare.