Support for color fonts has landed on version 27.0 (master).
Remaining issues:

* Fix font-hinting =--with-cairo=

See bug#35781.  Potentially useful reading:

- https://bugs.freedesktop.org/show_bug.cgi?id=11838
- https://unix.stackexchange.com/questions/321857/why-is-xft-ignoring-font-settings

* Check whether combining sequences work

For example:, regional flags, ZWJ sequences from

- ZWJ sequences from
  <https://unicode.org/emoji/charts/emoji-zwj-sequences.html>:
  - 🧟‍♂️, 🧟‍♀️
  - 🐕‍🦺
- regional indicators: 🇪🇺, 🇫🇷

* Add a convenient way to set a font for all emojis

AFAICT there is no convenient way to =set-fontset-font= e.g. Noto
  Color Emoji for "all emojis"; valid TARGETs for this function are
    - single characters
    - character ranges
    - scripts, as defined in =script-representative-chars=
    - charsets
    - nil = any character not already covered by another font-spec