The utility I used actually creates prodos files as well as png simulations. It’s been a while since I’ve used an apple emulator-- I’m not sure that any of the simulate the process well enough.
IIRC, Lord British hand edited the graphics to avoid pixel fringing–though few others were that perfectionist.
Pretty sure most emulators do the fringing, since it’s a software thing rather than a video artifact. I had a proper green monochrome monitor at home so I didn’t mess with color too much back then.
(I do remember being absolutely stunned when I first saw this though:)
The spectrum was well-understood as the crappier of the two. The fight, such as it was was between the C64 and the Amstrad CPC. The CPC had a more colorful palette and a much faster CPU, but (in a nutshell) lacked hardware sprites and scrolling, meaning that while it often looked better in screenshots, it played worse in the arcade-style titles that generally prevailed. And the C64 had SID on its side…
There’s an iPhone app that produces very decent output - ZXCam I think it’s called. A cool feature is that it can also output the generated image as a loading signal, for you to feed to an actual spectrum via your headphone jack.
They aren’t arbitrary - they are just the colours you get when each of the three RGB channels is either fully on or fully off. It makes the display logic very simple. It’s all about keeping costs down - you have to remember it cost about a third of the price of the C64.