samples/training/notify-user/res/values/styles.xml

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

    <style name="AppTheme" parent="android:Theme.Light" />

    <style name="NotificationText">
      <item name="android:textColor">?android:attr/textColorPrimary</item>
    </style>
    <style name="NotificationTitle">
      <item name="android:textColor">?android:attr/textColorPrimary</item>
      <item name="android:textStyle">bold</item>
    </style>
    <!-- If you want a slightly different color for some text,
         consider using ?android:attr/textColorSecondary -->
</resources>