IngredientListActivity.java

 private void toggleCheckboxesAndToolbar() {
        int colorId = adapter.showCheckboxes ? R.color.colorPrimary : android.R.color.darker_gray;
        myToolbar.setBackgroundColor(ContextCompat.getColor(this, colorId));

        MenuItem deleteMenuButton = myToolbar.getMenu().findItem(R.id.delete_menu_button);
        deleteMenuButton.setVisible(!deleteMenuButton.isVisible());

        adapter.showCheckboxes = !adapter.showCheckboxes;
        adapter.notifyDataSetChanged();
    }