What's the deal with Calendar Categories?
Why do all services and applications seem to handle them differently?
This is a general vent of me, working through all these things and trying to find a reasonable solution!

Situation

A bit of set up: I run my own B2B IT business. It's a small business, with just me as a full-time employee, but I have a business administrator (who just so happens to be my amazing wife) who handles some of the more admin-heavy workload i.e. Invoicing, general organisation, and some business communications.

Since the start of business operations back in 2015 (it's been nearly 11 years?! WOW) we've always been Open Source First, but due to the requirements of reliable email deliverability we [reluctantly] have been using Microsoft 365 as our primary Email and Calendar service.

Naturally, recent events with the dawn of "AI" and Microsoft's Copilot being shoehorned into absolutely everything that Microsoft have their hands on, we've made the very exciting decision to remove Microsoft 365 products from our business (Yay!).

The story of moving to another provider is one for another time, but suffice to say we are in the process of moving to a Open Source platform that utilises CalDAV for calendars.

Calendar Categories

We use categories to highlight different workloads... (well, my lovely administrator wife does anyway)... and previously, this was managed in Outlook (I'd like to make it clear I do not use Outlook myself).
For those that don't know, Outlook displays categorised calendar events by changing the colour of the entire event block in the calendar display, instead of placing a coloured strip/dot/line onto or alongside the event block like other products do.
And, of course Outlook does not work with CalDAV calendars so it's out. Fine, brilliant in fact. We'll use one of the birds (Thunder or Better).

"No big deal, right? It just looks diffent."
Sure, and we can use userChrome.css to make Thunderbird or Betterbird fill in the entire calendar entry with the category colour.

Anyway, it got me thinking...

How do other people actually use categories in their calendars?

You only need to look up a screenshot of any calendar application and you will see pictures of calendars with multiple coloured events spotted all over it, but, trust me, I've tried A LOT of these apps, and none of them get the colours from the categories. In most cases, the colours from the colour the calendar itself is set to.

So...

Are people using different calendars for different types of event?!

In which case...

What's the point in the categories?! Are categories just relegated to a life of being a barely visible line or dot on an event?

They're serious questions - I'd love answers! Please, let me know. Honestly.

Android

Thunderbird/Betterbird works well enough for our use on PCs, and that's fine, but don't even get me started on Android calendars... I have not found any (except Outlook, but no CalDAV in Outlook) that can colour an event based on its category. Some allow you to colour a specific event a different colour, but this isn't category based, it's single-event only.
I've not even seen a category field in an Android Calendar event, even though I know it's synchronised with DAVx⁵.

Questions

So, to offer this up to the world for responses to help me understand and plan a reasonable replacement system:

How do you set up and manage your calendars where multiple colours for different event types are required? Categories or different calendars?

Please add comments to this post on the Fediverse.

Thanks,