Set track drawable to null to remove grey track.

    <style name="DialtactsActivityTheme" parent="DialtactsTheme">

        <item name="android:actionBarStyle">@style/DialtactsActionBarWithoutTitleStyle</item>

        <item name="android:fastScrollThumbDrawable">@drawable/fastscroll_thumb</item>

        <item name="android:fastScrollTrackDrawable">@null</item>

    </style>

    <style name="CallDetailActivityTheme" parent="DialtactsThemeWithoutActionBarOverlay">