The Doctor is changing the desktop setting. There, in-universe explanation which has precedent within the show.
Oh, please, all the console room changes have been "just because."
They didn't even need to use such a pedestrian phrase, "desktop theme", as it doesn't describe the function very well either - the only thing approaching a "desktop" is one of the console panels. Not everything including the whole of the interior. Considering how modern Who has come up with genuinely brilliant coined terms like "fixed point in time" and "time can be rewritten", fluff like "muh desktop theme" is incredibly underwhelming.
The set changed over the years because various wall or prop parts got damaged in storage. Between 1963 and 1989, the only original set piece left were the inner doors; even the frame holding the doors in was replaced...
That one is a completely different design, whereas the Master's was a darkened version of the Doctor's console room.
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They took off the roundel discs and set moldings, spray painted them black, put them back on, filmed, then went back to repaint them all white again.

What the hell's wrong with using Ruth's TARDIS interior?! It was fantastic!
It's not "BIG AND EPIC ENOUGH" for modern audiences. Like Queen Xanxia trying to become immortal and not quite getting there, the same can be sets for the modern show if all they have to run on is how sexy the sets look.
Wow. I haven't been there since around 2006-7 when they stopped people posting even clearly marked Spoilers but looks like they're still the same idiots. Posting the video or photos will in no way cause anything to be shut down. If it did Twitter would have died long ago.
They've been increasingly inconsistent regarding their rule on youtube videos clips and the number of people breaking it in recent years. I wouldn't call them "idiots", but the moderators and others there all volunteer and for all the things they have to deal with, it's definitely not as much a priority compared to other things anymore.
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