Notmuch Colours

OK, I've got it (I'm not sure I entirely understand, but...) I have individually coloured tags
it's all to do with the tag transforms -- it's a little complicated...
have a look at the 'tag-transforms' and 'tag-formats' in the config file: https://www.neomutt.org/feature/custom-tags#neomuttrc
imagine you have emails notmuch-tagged/labelled with 'inbox', 'invites', 'replied'
this command allows you to abbreviate/iconise the tags:  tag-transforms inbox i  invites CAL  replied ↻
this command allows you to create expandos (%-things) for *individual* tags:  tag-formats inbox GI  invites Gi  replied GR
you can now use %GI %Gi %GR in your index_format string
finally, you can colour *these* expandos using: color index_tag, e.g.
color index_tag red default inbox
color index_tag cyan default invites
%GI transforms 'inbox' to 'i' and the color statement makes it red
it's a bit complicated, but it's very versatile