Dbug, Mike, yes, you are right and from point of view of the "whole picture" we mean actually the same thing! This is good!
I'll try to summarize the possibilities:
1) Direct connection
Pros: high speed, simple hardware, simple to program.
Cons: 8 colors, additional colors possible but little unpredictable, need experimenting to guess its capabilities.
2) 4-bits ladder
Pros: 16 shades of each color - theoretically 16*16*16=4096 colors
Cons: depends on serial attributes
(Honestly, I am a bit confused how to program in this case...).
3) bit planes
Pros: 8 shades of each color - 512 colors, no serial attributes, possible extras with 4th Oric, simple to program
In this case the 4th Oric can be used as one of the following options:
- logical on/off for every pixel (for dynamic effects, fades, etc.);
- high/low palette - here will be tricky:
= using only black/white "control" pixels we can change simultaneously
the intensity of R,G,B for every single pixel thus 1024 colors(!) and easy to program;
= using any of the 8 colors to control the intensity of R,G,B individually
gives more colors but dependent on serial attributes (I can't calculate how many will be the colors and in my opinion the programming will be hell, but maybe it only looks difficult...).
So, I think to make all this 3 cases and using multiplexers to select one of them "programmatically".
Please, check the variants - it's possible that I'm missing something or maybe there are other possibilities...