Note: you can entirely customize chat colors. This is undocumented yet, but you can try this: in the modal, check «use curent theme colors», then you can try to manually change color values in the URL.You must use valid CSS color values, and they must be properly URL encoded.
You can use the [social_stream browser extension](https://github.com/steveseguin/social_stream#readme) to mix multiple chat source (from Peertube, Twitch, Youtube, Facebook, ...) and include their contents in your livestream.The compatibility with this plugin was added in recent versions.
In the "plugin settings" tab, there is a "{{% livechat_label use_chat %}}" checkbox.Just check or uncheck it to enable or disable the chat associated to your video.
On the instance level, Peertube's administrators can choose if chat rooms are unique per video, or if there will be an unique chat room per channel.Please contact your instance's administrators for more information on how they configure the livechat plugin.