Can you link to some docs about this if possible?

And you are sure it does not set any more common environment variable for this? For example COLORTERM.

cc @kovidgoyal 👋🏻 Does Kitty term indicate truecolor support using any of the already-supported variables? Or does it really define its own terminfo database entry as indicated by the PR?

What already supported variables? It sets COLORTERM=truecolor. And has setrgbf and
setrgbb in its terminfo. And setaf and setab.

We don't check the terminfo database here, just environment variables. Good to know, thank you!!!

@AprilArcus can you verify that COLORTERM is indeed set to truecolor and show us a reproduction that this is being ignored?

COLORTERM is set to truecolor on localhost, but that environment variable does not survive when SSHing to a remote host. TERM does, however:

gnosis% echo $TERM $COLORTERM
xterm-kitty truecolor
gnosis% ssh sophos
Last login: Mon Aug 29 14:02:58 2022 from 172.253.30.65
ril@sophos ~ % echo $TERM $COLORTERM
xterm-kitty

(gnosis is my localhost (macOS 12.5.1, zsh 5.8.1) and sophos is my remote (Linux 5.17.11, zsh 5.9))

Fair enough. To work around this, you could also do ssh -o SendEnv=COLORTERM, or set it up in your ssh_config.

I don't control /etc/ssh/sshd_config on the remote end

That answer is referring to your local ~/.ssh/config file.

God I hate SSH for this. Yeah @sindresorhus this is a rather annoying limitation of SSH. I 👍🏻 this PR. Can't believe we're still dealing with this issue in 2022 but here we are.

Then on the server, make sure to allow client to pass certain environment variables in your /etc/ssh/sshd_config config file:

AcceptEnv LANG LC_* FOO BAR*

You shouldn't rely on env vars for detection. Both sudo and ssh dont pass them through. I would recommend you turn on truecolor by default and only turn it off with a blacklist for the few terminals that dont support it based on TERM. In 2022 most terminals support it.

@AprilArcus If you use the ssh kitten in kitty, it will pass COLORTERM through ssh magically even without needing to modify sshd_config