It's is really neat to see this being worked on. I seem to recall in the past I made a post how it was impossible to tune Altirra to display the correct colors in Ultima-IV. It seems impossible to get the landscape and water color combo to make sense. One would be brown, the other green. Or blue land and purple water. Something like that. The last screenshot shows an Apple II and displaying the colors as the developer intended.
I'm familiar with how this is generated in the Apple II circuit, not so much the Atari 800. The Apple II is sometimes spoken of as having false color, it can only tickle the Luma component. It knows nothing of Chroma. The circuit was the result of cost-cutting and simplicity. Back when IC chips were still expensive and consumed a lot of board space. Apple II had few analog parts. I remember being totally amazed that Atari had custom chips (TIA and GTIA) that were so versatile just a year or two later
For those of you wanting to experiment seeing the effects of all this, play around with the Artifacting Phase adjust slider in the color palette tuning dialog. And don't forget to turn artifacting to high in the video drop-down.
In Flight Simulator II it looks like it can be adjusted to what it's supposed to be.
FS2.zip 79.9KB 24 downloads
Here we have none. And phase slider does nothing. The artificial horizon and instrument panel numbers appear to be higher resolution than the out-of-the-window view. As it should be.
And here we turn it on and adjust the phase to various points. Notice how the out-of-the-window view doesn't change much. My color picker tool says the RGB values vary by about 6 or 7 each. Theoretically they shouldn't change at all.
Notice how adjusting L+C color has no effect on artifacting. The false colors are rock solid compared to the out-of-the-window view. As it should be.
But in Ultima IV I can't get the right combination.
The Apple II outputs what I believe to be the correct colors, green landscape, and blue water. It's remarkable and interesting to see how similar the two systems are in terms of resolution in these funky non-standard modes.
TRIVIA: IIRC the 1084S monitor has a "color-killer" circuit that can be turned on/off by a front-panel switch. It either processes L+C together for color graphics with a bit of smearing and artifacting. Or it asks for separate L and C, giving you a sharper B/W display, like for 80-columns, provided you are feeding composite into the L connector only. And here it displays FS2 like in the first example screenshot.