Normal SF&F tags are all one color (blue with a lighter blue background):
But META.SF&F tags are all over the place:
What do the different colors (text and background) mean?
Looking at the legend on the /tags page, we see the following key:
this is a moderator tag, it can only be added by a diamond moderator.
This includes tags like “faq”, any “status-XYZ” on feature requests and “community-ads”.
[dark grey: required-tag]
this is a required tag; every new question must have at least one required tag.
Namely “discussion”, “bug”, “feature request” and “support”.
[light grey: tag]
this is a standard tag; every question must have at least one tag.
These are analogous to the tags on SFF.se – they can be created, added and removed by any user (subject to rep requirements around tags/editing).