Unsure about time scales but in addition to the white and off cream there was ...

Ambra who made machines which were mostly light grey (both the metal and plastics) which was mid 90's from what I recall.
The Apple G3 which was made in a wide range of, lets go with eye catching, transparent colours.

define normal.

I worked as a tech in a PC repair shop from 1992 to 1997 and there were so many shades of beige, yellow, whitish and almond cases it was mind numbing so yeah, all of the above. Of course you had the dark yellow "I smoke nine packs a day" cigarette enhanced cases as well, but those were also yellow inside with yellow dust and a rank yellow smell.

Beige was the standard case color in early 1990's and before, only later white became more common and then black.

Azarien wrote:

Beige was the standard case color in early 1990's and before, only later white became more common and then black.

There was a very brief period of everything silver. And many cases had hybrid colors.
The FS OEM case that housed my Barton 3200+ is actually gray with black optical drives and a small portion of the front bezel also having some black.
Btw, there were also gray optical drives and floppy drives, but those were from before the silvery cases.

I remember there even being black-bezeled 5.25in floppy drives and some 2.88MB floppy drives seemed to come with black bezel.

I don't remember cases becoming white before going black. The aspirine-white only arrived after black had been "the norm" for a while already.

Personally I like the beige cases from the 2k's the most, when they were being made out of steel (I'm thinking kinda AOpen H600).
After black cases had been the norm for a while, they started making more cases that had more resemblance to a christmas tree and I don't like those. I also don't really like the PSU being mounted below, but it does seem to present better cooling solutions.

Is there actually somewhere where the history of the PC case is told?

It's kind of amusing because, if you want your entire PC to have the same colour, it can be a major pain in the ass 🤣 . Nothing is uglier than having a PC with the case, monitor, keyboard and mouse all being in different shades of yellow-ish white.

I remember when in 2001 I decided to put together my very first own PC from scratch and I picked out this black case with chromed front. That was at the start of when special cases were beginning to break through and everyone who saw my PC was like "OMG is that a computer? How cool!" while theirs still had the bog standard beige plastic look.