Signal-Android/res/values-v21/themes.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <style name="TextSecure.DarkTheme" parent="@style/TextSecure.BaseDarkTheme">
        <item name="android:navigationBarColor">#ff010101</item>
    </style>

    <style name="TextSecure.DarkNoActionBar" parent="@style/TextSecure.BaseDarkNoActionBar">
        <item name="android:navigationBarColor">#ff010101</item>
        <item name="android:colorControlActivated">@color/signal_primary_dark</item>
    </style>

    <style name="TextSecure.MediaPreview" parent="@style/TextSecure.BaseMediaPreview">
        <item name="android:navigationBarColor">@color/media_preview_bar_background</item>
    </style>

</resources>