Fixed slightly differently.

Kronolith 4.2.6

Changes have been made in Git (FRAMEWORK_5_2):

commit 6e9741802c58a5834fd3a13e303004682956c578
Author: Michael J Rubinsky <mrubinsk@horde.org>
Date:   Wed Apr 15 10:33:35 2015 -0400

     Bug: 13951 Allow background to be provided by the listTimeObjects API.

  kronolith/lib/CalendarsManager.php |   12 ++++++++++--
  1 files changed, 10 insertions(+), 2 deletions(-)

http://github.com/horde/horde/commit/6e9741802c58a5834fd3a13e303004682956c578

Changes have been made in Git (master):

commit 7e3dc75d8121929f8d9df911045724d8879bf9c6
Author: Michael J Rubinsky <mrubinsk@horde.org>
Date:   Wed Apr 15 10:33:35 2015 -0400

     Bug: 13951 Allow background to be provided by the listTimeObjects API.

  kronolith/lib/CalendarsManager.php |   12 ++++++++++--
  1 files changed, 10 insertions(+), 2 deletions(-)

http://github.com/horde/horde/commit/7e3dc75d8121929f8d9df911045724d8879bf9c6

When implementing a custom module that adds new categories and events 
through the listTimeObjectCategories() / listTimeObjects() API, I 
noticed that Kronolith does not display the background color that is 
defined by my categories, but uses the default one instead. When 
accessing the calendar a second, third, etc time, my background color 
is displayed correctly for the events of the respective category and 
the category itself in the sidebar.

After some investigation I found that Kronolith_CalendarManager does 
not set the background color attribute when it creates 
Kronolith_Calendar_External objects for every externally provided 
category. It fails to do so only the first time as the category info 
is cached in the session (including bg color). On second and further 
calls, Kronolith_Calendar_External objects are created from the cached 
version, including the background color attribute. Hence, the bg color 
of external calendars is only displayed when the cached version is used.

Here is the fix:

Replace this line in kronolith/lib/CalendarsManager.php:

                     $this->_allExternal[$api . '/' . $name] = new 
Kronolith_Calendar_External(array('api' => $api, 'name' => 
$description['title'], 'id' => $name, 'type' => $description['type']));

with

                     $this->_allExternal[$api . '/' . $name] = new 
Kronolith_Calendar_External(array('api' => $api, 'name' => 
$description['title'], 'id' => $name, 'type' => $description['type'], 
'background' => $description['background']));