Is it possible to customize the message thread layout? 

When you go to the task form, at the right hand side you can see the message thread.

Notes and System Notifications have the same layout, while Messages have a green background. We would like to modify the layout a little bit so that the Notes are also in a different background-color. 

I was able to add fields to the left hand side of the screen, but cannot find the view for the message thread. Nor is it possible to change the view with Odoo Studio.