I tried to modify the currently used style so that it draws a colored border around an album (in album list) indicating there're some new photos. New, by date and should be configurable: a week/a month, etc. Plus, it would be great to do the same with completely new albums (even empty).
I tried to edit index.php and themes.inc.php but without success :-\
Could anyone please help me?
Don't edit include/themes.inc.php. Edit themes/yourtheme/theme.php instead. Related to theming, moving accordingly.