Refer to documentation, there is no props to change the color of message bubble.

So if i want to implement this feature, which way is better? loading custom css file or using style tag in javascript? And is there some basic examples?

I know little about those front-end things. But i think it can be done by adding a param to Message or MessageGroup component. like:

<Message model={{ message: "Hello", sentTime: "just now", sender: "Bob" }} style=... (or className=...) />