packages/SystemUI/res/values-night/colors.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2018 The Android Open Source Project
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~      http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License

  NOTE: You might also want to edit: core/res/res/values-night/*.xml
  -->
<resources>
    <!-- The color of the material notification background -->
    <color name="notification_material_background_color">@*android:color/notification_material_background_color</color>

    <!-- The color of the legacy notifications with customs backgrounds (gingerbread and lollipop.)
    It's fine to override this color since at that point the shade was dark. -->
    <color name="notification_legacy_background_color">@*android:color/notification_material_background_color</color>

    <!-- The color of the material notification background when dimmed -->
    <color name="notification_material_background_dimmed_color">#aa212121</color>

    <!-- The color of the dividing line between grouped notifications while . -->
    <color name="notification_divider_color">#000</color>

    <!-- The background color of the notification shade -->
    <color name="notification_shade_background_color">#181818</color>

    <!-- The color of the ripples on the untinted notifications -->
    <color name="notification_ripple_untinted_color">#30ffffff</color>

    <!-- The "inside" of a notification, reached via longpress -->
    <color name="notification_guts_bg_color">@*android:color/notification_material_background_color</color>

    <!-- The color of the text inside a notification -->
    <color name="notification_primary_text_color">@*android:color/notification_primary_text_color_dark</color>
</resources>