How can I change the background color of a spinner popup?

None of the above solutions worked for me.

The solution was writing in the adapter passed to the spinner a different implementation in the method getDropDownView to display a different layout with custom colors:

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View vista = convertView;       

    // layout for spinner widget

    if (vista==null) {
        LayoutInflater inflater = actividad.getLayoutInflater();
        vista = inflater.inflate(R.layout.fila_colores_spinner, null);                  
    }

    return vista;
}

@Override
public View getDropDownView(int position, View convertView,ViewGroup parent) {
    View vista = convertView;       

    //layout for spinner popup

    if (vista==null) {
        LayoutInflater inflater = actividad.getLayoutInflater();
        vista = inflater.inflate(R.layout.fila_colores_spinner_popup, null);                    
    }

    return vista;
}

Use android:popupBackground="@drawable/Yourxmlfile.xml" in Your spinner declaration of xml .

For Eg.

    <Spinner
        android:id="@+id/spinner3"
        android:layout_width="fill_parent"
        android:layout_height="40dp"
        android:layout_gravity="center"
        android:layout_weight="50"
        android:background="@drawable/gradient_spinner"
        android:gravity="center"
        android:paddingLeft="40dp"
        android:popupBackground="@drawable/radialfront"
        >