Index: src/wp-content/themes/twentyfifteen/inc/customizer.php
===================================================================
--- src/wp-content/themes/twentyfifteen/inc/customizer.php	(revision 30394)
+++ src/wp-content/themes/twentyfifteen/inc/customizer.php	(working copy)
@@ -28,9 +28,8 @@
 	) );
 
 	$wp_customize->add_setting( 'color_scheme_css', array(
-		'default'           => '',
-		'sanitize_callback' => 'esc_html',
-		'transport'         => 'postMessage',
+		'default'   => '',
+		'transport' => 'postMessage',
 	) );
 
 	$wp_customize->add_control( 'color_scheme', array(