On a few places on some child meta sites, the "other" tags (that is, ones like chat, not the moderator-only ones like status-review, and not the required ones like bug), are blue, while in most other places, they are grey.
This appears to be the same on all sites with unique Meta themes (only full-sites, I believe), but not on meta.stackexchange.com itself (where you are now) or other sites with the "default" theme.
Here is a list of places where they appear blue that I've found so far:
- /tags, in the legend/key for the colours
- When asking a question in the Tags field
Here is a screenshot of what it looks like on Code Golf - the two different colours are highlighted in pink:
The grey ones are too similar in style to the required tags, and aren't distinguishable from tags referring to the main site (
[meta-tag:foo] [tag:foo]). The difference is irrelevant here because there is no main site for non-meta tags to link to, but on Code Golf it looks like this).
The blue ones don't match the theme of the relevant sites, and I'm assuming they're using the default network colour.
IMO they should be the same as the general accent colour on meta (that's red on SO for example).