Should we be expecting a permanent update that includes multiple theme options under the Current theme setting?
I don't remember when or where this was mentioned, but there are valid reasons why it's not possible to edit/change the forum's default theme.
At the time the forum was created, and the underlying software used, the layout was intertwined with the forum's operational code. Well, unlike what is done today in web development, where the layout almost never interacts with the functional code of a website.
Since the forum software was customized for security reasons and more, creating a new theme would involve replicating all those changes twice. This means that any future updates or adjustments would have to be done in duplicate to truly guarantee complete security across both themes. This scenario generated duplicate maintenance work and duplicate potential failures.
Furthermore, if I'm not mistaken, this active functionality could also be an entry point for some kind of attack on the forum, due to the very underlying system used by the forum.
Therefore, for security reasons, this function is disabled, and there is no option to change the theme.
Changing the color for a day isn't difficult because it's managed internally and has a short duration, avoiding future maintenance.
In short, for security reasons, we maintain the traditional theme of our forum, allowing you to have a continuous experience from the first day the forum was created.