https://wordpress.stackexchange.com/q/282425/8521

background-color-partial.js

/* eslint consistent-this: [ "error", "partial" ] */

wp.customize.selectiveRefresh.partialConstructor.background_color = (function( api, $ ) {
	'use strict';

	return api.selectiveRefresh.Partial.extend( {

		/**
		 * Refresh.
		 *
		 * Override refresh behavior to apply changes with JS instead of doing
		 * a selective refresh request for PHP rendering (since unnecessary).
		 *
		 * @returns {jQuery.promise} Resolved promise.
		 */
		refresh: function() {
			var partial = this, backgroundColorSetting;

			backgroundColorSetting = api( partial.params.primarySetting );
			_.each( partial.placements(), function( placement ) {
				placement.container.css( 'background-color', backgroundColorSetting.get() );
			} );

			// Return resolved promise since no server-side selective refresh will be requested.
			return $.Deferred().resolve().promise();
		}
	} );
})( wp.customize, jQuery );

wpse-282425.php

<?php
/**
 * Plugin Name: WPSE 282425: Edit shortcuts for partials without selective refresh
 * Plugin URI: https://wordpress.stackexchange.com/q/282425/8521
 * Author: Weston Ruter, XWP
 * Author URI: https://make.xwp.co/
 * License: GPLv2+
 */

namespace WPSE_282425;

const DEFAULT_BACKGROUND_COLOR = '#43C6E4';

/**
 * Render partial.
 */
function render_partial() {
	?>
	<div id="bg-color" style="padding: 3em; background-color: <?php echo esc_attr( get_theme_mod( 'wpse_282425_background_color', DEFAULT_BACKGROUND_COLOR ) ); ?>">
		The background color on this can be edited via an edit shortcut without doing any server-side partial refresh request.
	</div>
	<?php
}

// Put it on the page so we can see it.
add_action( 'wp_footer', __NAMESPACE__ . '\render_partial' );

/**
 * Register Customizer constructs.
 *
 * @param \WP_Customize_Manager $wp_customize
 */
function customize_register( \WP_Customize_Manager $wp_customize ) {
	$section = $wp_customize->add_section( 'wpse_282425' , array(
		'title' => 'WPSE 282425',
		'priority' => 30,
	) );

	$wp_customize->add_setting( 'wpse_282425_background_color' , array(
		'default' => DEFAULT_BACKGROUND_COLOR,
		'transport' => 'postMessage',
		'sanitize_callback' => 'sanitize_hex_color',
	) );

	$wp_customize->add_control( new \WP_Customize_Color_Control( $wp_customize, 'wpse_282425_background_color', array(
		'label' => 'Background Color',
		'section' => $section->id,
		'settings' => 'wpse_282425_background_color',
	) ) );

	$wp_customize->selective_refresh->add_partial( 'wpse_282425_background_color', array(
		'type' => 'background_color', // 👈 Needed to connect this PHP-registered partial with the corresponding partialConstructor in JS.
		'selector' => '#bg-color',
		'container_inclusive' => true,
		'render_callback' => __NAMESPACE__ . '\render_partial',
	) );
}
add_action( 'customize_register', __NAMESPACE__ . '\customize_register' );

/**
 * Enqueue scripts.
 */
function enqueue_scripts() {
	if ( ! \is_customize_preview() ) {
		return;
	}
	\wp_enqueue_script(
		'wpse282425-background-color-partial',
		\plugin_dir_url( __FILE__ ) . 'background-color-partial.js',
		array( 'customize-selective-refresh' )
	);
}
add_action( 'wp_enqueue_scripts', __NAMESPACE__ . '\enqueue_scripts' );