Dual license the colours of the Modus themes?

[Protesilaos Stavrou <info@protesilaos.com>]

Hello everyone,

The modus-themes (modus-operandi, modus-vivendi) are distributed under
the terms of the GNU GPLv3 and are part of Emacs.  I was wondering
whether their colours could be licensed under different terms, such as
by putting them in the public domain (with Creative Commons).

I am reading the GNU commentary on licenses[1] and understand that my
choice will have to be compatible with the GPL.  What I am not sure
about are the following:

* Is it possible to keep the modus-themes under the GPL but also
  dedicate its colours to the public domain?

* Does the inclusion of the modus-themes in Emacs impose any constraints
  on the possibility of such a dual license arrangement?

If there is any precedent or resources I could refer to, please let me
know.

I intend to do what is good for Emacs and, by extension, GNU: if a dual
license for the colours of the modus-themes can cause problems for
Emacs, then I will simply not do it.

As for why I am asking this: there are cases where someone wants to
reuse the colours of the modus-themes---just the colours---for stylistic
purposes and there is uncertainty whether they are allowed to do so
under the terms of the GPL.

All the best,
Protesilaos (or simply "Prot")

[1] <https://www.gnu.org/licenses/license-list.html>

-- 
Protesilaos Stavrou
https://protesilaos.com