I had exactly the same problem and managed to change the text color by editing the color value the library itself from Eclipse. This assumes that you have imported the library in Eclipse and that it should be visible from the package explorer window.
Navigate to: [Library package] -> [res] -> [values] -> [styles.xml].
Now, change this:
<style name="TextAppearance.ShowcaseView.Detail" parent="android:style/TextAppearance">
<item name="android:textColor">#FFFFFF</item>
</style>
Into this:
<style name="TextAppearance.ShowcaseView.Detail" parent="android:style/TextAppearance">
<item name="android:textColor">#000000</item>
</style>