finished (subject to deciding I want to finesse colours some more)

References (I am absolutely expecting all of these to bitrot, probably in fairly short order, but oh well):

• an eBay listing clearly showing the colour codes (which I wound up more-or-less ignoring) as well as the whole pattern (which I didn't)
• an Etsy listing with lots of partial, but clear, photos
• a Pinterest pin

Software: minor fucking around in GIMP; majority of both attempts in Pixelorama.

The one bad thing I have to say about Pixelorama (... other than the fact that it crashed repeatedly, but hey, its autosaving and recovery were rock-solid) is that I couldn't find any way to banish the once-a-minute "File autosaved..." notifications that popped up in the bottom left corner and then kept rising as they faded out (and similar: effects of ctrl+z, actual saving, ...).

"Huh," said A, "I'm surprised at that, it's the sort of thing I expect to see in old computer games."

"... it is dedicated software for pixel art," I replied.

Good point well made, came the approximate response.

Possibly I will even tip the project.