If you want to create a Category there are two available options. The first one is creating a Category that can used again and again. The second method is for creating a special one off Category.

Method 1.

• Settings > Calendar
• scroll down to 'Categories' section

To create a new Category:

• click on 'New'
• Give it a suitable name
• Select checkbox to 'Use Colour'
• Click in the colour checkbox
• choose a colour and click on OK
• Click on 'OK' to create.

To Edit a colour of an existing category:

• Select the category in the list and click on Edit.
• Click on the coloured box
• choose a colour and click on OK
• Click on 'OK' to save.

Method 2. Single use Category In 'Calendar' Click on 'New Event' Category: - click on drop down to see list of current saved categories. At the top of that list is 'Add a new Category' In that text area type name of category and press 'Enter' key on keyboard. That category will now appear in 'Category' text box.

If you save the Event and later go back and open it again. In the Category drop down list you will see that name of the special one off category and it will have a tick showing it was selected. But if you then clickon 'New Event' again - that special one off category will not be available. You would need to recreate it. But if you find you need to use it frequently then it's probably a lot easier to create it via Settings > Calendar as mentioned in method 1.

Excellent! Now is there a way to change the background color of the calendar events? I have the TB calendar pulling events from 3 different Google calendars and they each show up with a different background color.

I am having a whole heap of issues with Categories as well. I've tried deleting them all to add my own, but they reappear on each restart of TB. The trick was to rename them first, then deleting them seems to work. Another issue is that if you then assign a custom category to an event, then rename the category, both the old-name and new-name categories appear as options in the category dropdown of the event. Until you restart TB. Seems mostly a cache issue, but it feels buggy.

Using Windows 10 OS and Thunderbird version 128.8.0 esr originally downloaded from the official Thunderbird website and profile stored in the default location. Not using anything from the Windows app store which does effect profile location etc. Not using any addon extension that may cause an issue with Categories which is used for Events and Tasks.

I'm not having any difficulty deleting any Category from: Settings > Calendar in 'Categories' select unwanted category and click on 'Delete'.