Hi Juri,

Thank you very much for the detailed test case.
> Previously I tried in the MATE terminal emulator,
> but xterm-256color was an essential detail indeed.
> Now I was able to reproduce with TERM="xterm-256color"
> and to track down the source of this problem.
>
> It happens while the color "ForestGreen" is loaded for
> the face font-lock-type-face that has this definition:
>
>   (((class color) (min-colors 16) (background light))
>    :foreground "ForestGreen")
>
> by tty-color-canonicalize.
>
> Could you please try this patch to see if it fixes the problem:
>
> diff --git a/lisp/term/tty-colors.el b/lisp/term/tty-colors.el
> index 307586f221..5af8170203 100644
> --- a/lisp/term/tty-colors.el
> +++ b/lisp/term/tty-colors.el
> @@ -820,7 +820,7 @@ tty-color-canonicalize
>    "Return COLOR in canonical form.
>  A canonicalized color name is all-lower case, with any blanks removed."
>    (let ((case-fold-search nil))
> -    (if (string-match "[A-Z ]" color)
> +    (if (string-match-p "[A-Z ]" color)
>         (replace-regexp-in-string " +" "" (downcase color))
>        color)))
>

Thank you for root-causing this! The patch you provided does indeed fix the
issue for me.

Best,
Jayden