Perpetuate the original sin of dark theme

Fixes #7614

res/layout/invite_activity.xml

@@ -14,7 +14,7 @@
                       android:layout_width="match_parent"
                       android:orientation="vertical"
                       android:padding="10dp"
-                      android:background="@color/signal_primary">
+                      android:background="?attr/invite_background">
 
             <ImageView android:id="@+id/heart"
                        android:layout_width="wrap_content"

res/values/attrs.xml

@@ -87,6 +87,8 @@
     <attr name="import_export_item_background_shadow_color" format="reference|color" />
     <attr name="import_export_item_card_background" format="reference" />
 
+    <attr name="invite_background" format="color"/>
+
     <attr name="reminder_header_background" format="color"/>
 
     <attr name="menu_new_conversation_icon" format="reference" />

res/values/themes.xml

@@ -233,6 +233,7 @@
         <item name="preferenceTheme">@style/PreferenceThemeOverlay.Fix</item>
 
         <item name="search_toolbar_background">@color/white</item>
+        <item name="invite_background">@color/signal_primary</item>
     </style>
 
     <style name="TextSecure.DarkTheme" parent="@style/Theme.AppCompat">
@@ -355,6 +356,7 @@
         <item name="group_members_dialog_icon">@drawable/ic_group_white_24dp</item>
         <item name="preferenceTheme">@style/PreferenceThemeOverlay.Fix</item>
         <item name="search_toolbar_background">@color/black</item>
+        <item name="invite_background">@color/black</item>
     </style>
     
     <style name="RationaleDialog" parent="Theme.AppCompat.Light.Dialog.Alert">