Fixed. For some reason Apache crashed, resulting in that error message.
If in future anyone will see any errors on colorizeit.com, please send me a message here or on my forum.
Later this year colorizeit.com website may be removed. That website no longer has a purpose: latest phpBB styles are available in official styles database so there is no point in keeping colorizeit.com copy, styles for other software will have their own modern editor built in directly in forum as add-on. However integration with phpbb.com styles database should continue working.