We had the same issue. Standard WordPress loads farbtastic.css only for the admin back-end. If blocking /wp-admin in .htaccess (e.g. by using Better WP Security) gives 404’s on wp-admin/css/farbtastic.css, there must be a plugin on the front-end to cause this. One of the plugins known to cause this is Ultimate Landing Page and Coming Soon Page. Do you have that plugin? If so, you should deactivate it when your site is live.
