Rated 4 out of 5 stars

Now I can see event by category color only (and do not see calendar color at all) :(

Can I see both colors in event (50/50): 1 - calendar, 2 - category?

This review is for a previous version of the add-on (4.0). 

With the latest version of Calendar Tweaks, you have the option to color event backgrounds with the category color, instead of the normal calendar color.

This feature can be enabled/disabled as follows:

- Select Tools on the Thunderbird main menu, and then select Add-ons to show the Add-ons Manager
- Select the Extensions tab
- Click on the Options button in the Calendar Tweaks entry
- Enable or disable the "Apply category color to event backgrounds" option.