The Bug:

Local game hosting messages aren't prefixed with gray color indicators despite being system messages.

The 1.19.1 Pre-release 4 changelog states that

System message are now displayed with a gray color indicator

This means that any messages that are displayed by the system, for example, command feedback messages, are prefixed with gray color indicators. Despite messages displayed through opening a world to LAN (when not using the "/publish" command) being considered system messages, they are not prefixed with gray color indicators.

Steps to Reproduce:

• Join a singleplayer world and display a system message in chat by adding a tag to yourself by executing the following command.

• /tag @s add test

• Take note of how the command feedback message is correctly prefixed with a gray color indicator as it's a system message.
• Open your world to LAN by pressing ESC > Open to LAN > Start LAN World and look at the message displayed in chat.
• Take note as to whether or not local game hosting messages are prefixed with gray color indicators.

Observed Behavior:

Local game hosting messages aren't prefixed with gray color indicators despite being system messages.

Expected Behavior:

Local game hosting messages would be prefixed with gray color indicators.