They are colored, you just have to set it in the settings :-)

Hmm,

I could not find anything about calendar colors in the settings pages

• Not in the global settings
• Not in the global calendar settings
• Not in the calendar specific settings

did I miss another settings page

no, you got them all.
It is in the calendar specific settings.
Choose "Properties" then click on the paint bucket before the name of the calendar.
Now choose the desired color and press "Save".

I just found out myself and realized what the icon there means.

The issue can be closed.

Thank's for your help.