When I suggested moving away from a third-party event application to a Discourse-integrated solution for my community, I was asked to keep a color-per-tag feature.
It was not available, either in Discourse Calendar or in Pavilion’s Events plugin, which I modified a bit as a proof of concept to add this feature in an ugly, hard-coded way: Events Plugin 📆 - #699 by Canapin.
I ended up not using any of them for several reasons, the missing color feature being one of them. 