How to overload the update() of existings widgets?

Problem: I couldn’t overload the update() method of an existing widget. The widget method and the form method work fine but I can’t update the value of the new options defined in the form method.

Bellow is how I made that:

I want to use the default WP widgets from my custom theme and I need to give them the look and feel of my company.

I inherited the WP_Widget_Pages class and overloaded the form() (I need to add two options), the update (to manage the new options) and the widget() methods.

In my functions.php it look like this :

function load_my_widgets() {
register_widget('WP_MY_Widget_Pages');
}

/* Add our function to the widgets_init hook. */
add_action( 'widgets_init', 'load_my_widgets' );

class WP_MY_Widget_Pages extends WP_Widget_Pages {

function widget( $args, $instance ) {
    parent::widget($args, $instance)
}

function update( $new_instance, $old_instance ) {
    $first_instance = parent::update($new_instance, $old_instance);
    $first_instance['block_type'] = 'my_block_type';
    $first_instance['block_color'] = 'my_block_color';

    return $first_instance;
}

function form( $instance ) {
    //Defaults
    $instance = wp_parse_args( (array) $instance, array( 'sortby' => 'post_title', 'title' => '', 'exclude' => '', 'block_type' => '', 'block_color' => '' ));
    $block_type = esc_attr( $instance['block_type'] );
    $block_color = esc_attr( $instance['block_color'] );
    parent::form($instance);
    ?>
        <p>
            <label for="<?php echo $this->get_field_id('block_type'); ?>"><?php _e( 'Block type:' ); ?></label>
            <select name="<?php echo $this->get_field_name('block_type'); ?>" id="<?php echo $this->get_field_id('block_type'); ?>" class="widefat">
                <?php foreach (get_all_block_type() as $block_label => $block_type): ?>
                    <option <?php selected( $block_type , $instance['block_type'] ); ?> value="<?php echo $block_type; ?>"><?php _e($block_label); ?></option>
                <?php endforeach; ?>
            </select>
            <?php echo 'Block type : '.$instance['block_type']; ?>
        </p>
        <p>
            <label for="<?php echo $this->get_field_id('block_color'); ?>"><?php _e( 'Block color:' ); ?></label>
            <select name="<?php echo $this->get_field_name('block_color'); ?>" 
                    id="<?php echo $this->get_field_id('block_color'); ?>" 
                    class="widefat" style="background-color: <?php echo $block_color_value; ?>" >
                <?php foreach (get_all_block_color() as $block_color_label => $block_color_class): ?>
                    <option <?php selected( $block_color_label , $instance['block_color'] ); ?> value="<?php echo $block_color_label;?>" style="background-color: <?php echo $block_color_class;?>" >&nbsp;</option>
                <?php endforeach; ?>
            </select>
            <?php echo 'block color : '.$instance['block_color']; ?>
        </p>

    <?php
}

}

I have cleaned up the widget method for reading purpose.
I did not bother you with validation in the update(), I have set a literal value to make it short.

When I go to the dashboard/widget page, then display my Page widget, I can set values to the two new attributes. When I save, the output of the new option’s value shows nothing (there is nothing too in the database: select option_value from wp_options where option_id=’106′;)

I would really appreciate any hint.

Thanks in advance.