How to change color of Toolbar back button in Android?

You can add a style to your styles.xml,

<style name="ToolbarTheme" parent="@style/ThemeOverlay.AppCompat.ActionBar">
  <!-- Customize color of navigation drawer icon and back arrow --> 
  <item name="colorControlNormal">@color/toolbar_color_control_normal</item>
</style>

and add this as theme to your toolbar in toolbar layout.xml using app:theme, check below

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:minHeight="?attr/actionBarSize"
    android:background="?attr/colorPrimary"
    app:theme="@style/ToolbarTheme" >
</android.support.v7.widget.Toolbar>