Thunderbird colored calendar

Settings --> General --> Config Editor. Enable toolkit.legacyUserProfileCustomizations.stylesheets -> true

go to profile folder ~/.thunderbird/fjdkslfds.default-whatever

mkdir 'chrome'

create file userChrome.css

/* Calendar  - set event category colour instead of calendar colour */

.calendar-category-box{     margin:0 0 0 -200px !important;     min-width: 200px !important;     }    
.alarm-icons-box,.reminder-icon{     margin:0 0 0 0!important;     }    
.event-name-label,.item-time-label,.alarm-icons-box,.reminder-icon{     z-index:100000!important;     }     
.calendar-item-flex{     padding:0!important;     }     
.calendar-month-day-box-list-item{     margin:0!important;     }     
.calendar-color-box{     border:none!important;     }      
.event-name-label{     white-space:break-spaces !important;     }

Calendar now has correct category colors as background or the calendars source account color.