>I'm not sure I understand what this means. What is "agetty"?

Linux console login utility.

> And what do you call "emacs terminal"?

emacsclient -t (terminal mode) as noted in original post. Not -c option.

>M-: (display-color-cells) RET

8 : console

256 : xterm

>And what happens if you try to customize these faces to define the
>colors they should have?

It works! Tried it from the menu bar.

On Wed, Sep 8, 2021 at 10:02 AM Eli Zaretskii <eliz@gnu.org> wrote:

> From: RDS <rds1944@gmail.com>
> Date: Wed, 8 Sep 2021 09:46:38 -0700
> Cc: Lars Ingebrigtsen <larsi@gnus.org>, 50462@debbugs.gnu.org
>
> 1) Using standard agetty, not emacs terminal.

I'm not sure I understand what this means. What is "agetty"? And
what do you call "emacs terminal"?

> 2) M-x list-faces-display (after fault)
> All OK except
> font-lock-string-face (black-on-black)
> sh-escaped-newline "
> toolbar "
> window-divider-last-pixel "

And what happens if you try to customize these faces to define the
colors they should have? Or different colors? Does that work, or do
these faces fail to display any colors, no matter what?

Btw, how many colors does this terminal support? You can find the
answer like this:

M-: (display-color-cells) RET

And finally, does "M-x list-colors-display RET" show some colors
incorrectly?