Index: wp-content/themes/twentynineteen/functions.php
===================================================================
--- wp-content/themes/twentynineteen/functions.php	(revision 58931)
+++ wp-content/themes/twentynineteen/functions.php	(working copy)
@@ -342,7 +342,7 @@
 	?>
 
 	<style type="text/css" id="custom-theme-colors" <?php echo is_customize_preview() ? 'data-hue="' . absint( $primary_color ) . '"' : ''; ?>>
-		<?php echo twentynineteen_custom_colors_css(); ?>
+		<?php echo esc_html( twentynineteen_custom_colors_css() ); ?>
 	</style>
 	<?php
 }