Hi @Tilmn
Thank you for your question. We'd be interested to hear about the ideas you have for tweaking the default appearance of Mattermost!
Would you be interested in joining the Contributors Team to share more about your concepts? We'd love to see some mock-ups of what you have in mind.
Once you've signed up at the above link, please click on "More..." in the left-hand-sidebar below "Channels" and join the UX Design channel to start a discussion.
Thanks!