For example, setting minecraft_chat_format to a value that includes §1 does not color the chat prefix blue, but instead inserts an unknown character. Using "\u00A71" to create the same effect results in no change to the message (possibly getting sanitized out?).

Sorry if there's a way to do this and I'm just not seeing it.

Will investigate on this issue thanks for reporting

minecraft_chat_format = "<§1${member_nickname}§r> ${message}"

All other settings are defaults aside from allowing other bots to create messages.

It's on a remote host - I believe it's CentOS. Unsure about file encoding.

The above format results in this appearance:

https://i.imgur.com/rZuIHHN.png

Hi,
I tested with the following config :

and i ended with this result :

Can you share more detail about your configuration (config, maybe OS, file encoding) ?
You may also want to join my discord : https://discord.gg/rzzd76c

Solved replacing § by \u00a7