I want to keep it original. So other people wouldn't have the same design, and if all Conversations themes are the same in colour and variety then won't it make all them redundance?

You can change it to your preferences or taste in CSS file just swap them around. The problem is if you change the colour of the bubble then you'll have to change the font colour and for LINKs will not able show up in the bubble properly. I mainly focusing on readability than looks. Looks come after usability

No point of having flashy UI if it doesn't work properly right?