Underline color not working inside Neovim

[MunifTanjim]

Problem

echo -e '\e[4:3m\e[58:2::240:143:104mfoobarbaz\e[59m\e[4:0m\n'

Outside Neovim:

Inside Neovim:

Steps to reproduce

• Open neovim terminal: nvim --clean -c ':term'
• Run echo -e '\e[4:3m\e[58:2::240:143:104mfoobarbaz\e[59m\e[4:0m\n'

Expected behavior

Underline should have different color.

Neovim version (nvim -v)

v0.10.0-dev-2755+ge1ff2c51c-Homebrew

Vim (not Nvim) behaves the same?

N/A

Operating system/version

macOS 14.4

Terminal name/version

Kitty 0.33.1

$TERM environment variable

xterm-kitty

Installation

homebrew

[jespino]

I'm able to reproduce this same behavior in Linux with gnome-terminal in neovim 0.7.2

[justinmk]

Are we blocked by libvterm ?

[zeertzjq]

Yes