In fact it is pretty easy.All you should do is defining an attribute like this
<style name="tabtextcolor" parent="@style/Widget.Sherlock.ActionBar.TabText">
<item name="android:textColor">@android:color/white</item>
</style>
and then
adding these styles to your theme
<item name="actionBarTabTextStyle">@style/tabtextcolor</item>
<item name="android:actionBarTabTextStyle">@style/tabtextcolor</item>
