If theymos enable theme changing option in "Look and Layout Preferences", you might be able to change theme easily. I don't know if it was ever enabled and how it does, i.e. whether it is a drop-down list or an local/server upload option.
Look and Layout Preferences: https://bitcointalk.org/index.php?action=profile;u=profile;sa=theme
Look and Layout Preferences: https://bitcointalk.org/index.php?action=profile;u=profile;sa=theme
In the initial few months I joined, when avatars were also available, it was possible to change the theme of bitcointalk.
I don't remember exactly, but there was a couple of options/choices available. I think this was still the one I liked.
