Steps:
The color keeps applied to the group (which is nice!) but the color selector is not available anymore via Info. Maybe this is intended behavior, but it seems logical if both Ordinary tag and Group tag would have the color selector available.
(btw, changing it back to an Ordinary Tag brings back the color selector)
Only ordinary tags have a color property; groups do not.
That doesn’t seem congruent with the fact that Group Tags can have colors (see screenshot). Or am I wrong and should I call this an ordinary tag which is excluded from tagging (I thought those were called Group Tags). If the _meta item in this example also is called an ordinary tag than it would also have to have a color selector available (which it hasn’t)
That’s not a group tag. That’s merely a group located in the Tags group of a database. It is only a container and not applied as a tag to anything.
These are group tags, one with a custom color applied…
PS: I had just woken up and I think I misread your comment. But the fact still stands: groups do not have a color property. Your use of a group in the Tags group is an exception and I don’t know if it’s intentional. It looks like it just retained the color applied when it was a tag.
In fact, I just saw this is possible but @cgrunenberg would have to comment on it.…
That’s exactly how I’m using it - as a container without it being applied (useful in my situation, so hopefully it isn’t something that gets removed). As this is possibly my only observation was that when doing that the color selector isn’t accessible anymore.
Indeed, as groups don’t have a color property. I don’t think this it’s intentional the group retains the tag color, but it may be a serendipitous thing 
Let’s see what @cgrunenberg has to say 
On a sidenote: I do appreciate the fact that slashes are possible in tag names though if creating them manually, this gives a great way of integrating DT with Obsidian for me!
Properties aren’t reset, e.g. exclusions might be only temporarily toggled. But the color should of course be ignored while it’s excluded.