<?php 
// Bottom background color    
$wp_customize->add_setting(
    'bottom_background_color',
    array(
        'default'           => themesflat_customize_default('bottom_background_color'),
        'sanitize_callback' => 'esc_attr',
    )
);
$wp_customize->add_control( 
    new themesflat_ColorOverlay(
        $wp_customize,
        'bottom_background_color',
        array(
            'label'         => esc_html__('Backgound Color', 'norstar'),
            'section'       => 'color_bottom',
            'settings'      => 'bottom_background_color',
            'priority'      => 17
        )
    )
);