IIRC the desk side onyx had the royal purple stripes and only accepted one CPU board, the rack mount version were that blue-purple color, more indigo (color)
So there were two computers made with the same bits mid 90s. Origin(compute, blue) and onyx(graphics, purple). Both had deskside and rack systems.
Onyx had a few slots reserved for graphics, original could have more compute boards. But you could certainly put two couple cpu boards in an onyx deskside or rack.
It must have been more complex then that, I was at the skywalker ranch when onyx was being replaced by o200/2000 and never saw a purple onyx at Kerner(ILM), I had a purple Indy impact as my home machine and was looking for purple. I hated teal with a passion.
Perhaps all the purple rack onyx had been dumped but we dug through ILMs boneyard looking to add to our cxfs cluster, but the FC bus speed was too low.
It is possible that R10k was different or that there were multiple chassis. The desk sides I had experience with required RAM in slot 1, with CPU in slot 2, with up to 4 CPUs on the board.
o200 was more restrictive, with 2 CPUs per chassis, with the ability to cray-link two chassis for a total of 4 CPUs, more required o2000.
But this was a quarter of a century ago or more by now…so I may misremember things.
I actually forgot that they made a low end ‘Indy’ and never saw one. We called the Indigo2 Indy
There were some oddities with ad dollars and prestige clients in the 90s, where systems would be upgraded, avoiding swapping out the serialized, asset tagged parts, yet upgrading systems.
The teal Indigo2s were the original with the impact graphics ones being purple.
But all the Indigo2s I saw typically were r10k + max impact graphics despite the color.
The cases were identical.
But Evans & Sutherland and Lucas are the only places I dealt with SGI, so probably not a good source for typical customer’s experience