[android] How to change color of Toolbar back button in Android?

Just use the MaterialToolbar and override the default colors:

    <com.google.android.material.appbar.MaterialToolbar
        style="@style/Widget.MaterialComponents.Toolbar.Primary"
        android:theme="@style/MyThemeOverlay_Toolbar"
        ..>

with:

  <style name="MyThemeOverlay_Toolbar" parent="ThemeOverlay.MaterialComponents.Toolbar.Primary">
    <!-- color used by navigation icon and overflow icon -->
    <item name="colorOnPrimary">@color/...</item>
  </style>

enter image description here

If you are using the androidx.appcompat.widget.Toolbar or the MaterialToolbar with the default style (Widget.MaterialComponents.Toolbar) you can use:

<androidx.appcompat.widget.Toolbar
    android:theme="@style/MyThemeOverlay_Toolbar2"

with:

  <style name="MyThemeOverlay_Toolbar2" parent="ThemeOverlay.MaterialComponents.Toolbar.Primary">
    <!-- This attributes is used by title -->
    <item name="android:textColorPrimary">@color/white</item>

    <!-- This attributes is used by navigation icon and overflow icon -->
    <item name="colorOnPrimary">@color/secondaryColor</item>
  </style>