TL;DR
Create green and red variants of all signals that only read from/send to the corresponding network, when selecting signals in control UIs.What?
Quality introduces a new UI for creating modified signals that carry quality information.The same concept can be used to give each signal two additional variants, "red" and "green". These would be selected by an additional control in the signal selection UI, just like quality. It will use the same control used to select circuit colours currently in the combinators, and the icon will use the coloured background like when hovering over an electric pole. The default is both.
If a Red signal is selected, then the circuit logic for that signal will only look at the red network and ignore the green. If Grene is selected, the logic will only look at the green network and ignore the red. If both are selected, it behaves like currently.
The combinator specific colour selection UI will be removed, and when loading old saves, the selection will be transferred into the signal.
Ideally, this would open the door for mods to add a blue wire, or more.
Why?
This originates from this popular suggestion to support colour selection in more places. But since this is a specific idea of how to accomplish it, I figured it's worth a new thread. Doing it this way would be more work than adding individual circuit colour selectors, but it would mean that it only needs to be done once for all circuit-connected entities.The rationale is otherwise fundamentally the same as the other thread: there are many places where it's desirable not to "cross the streams" of the circuit network, but especially for certain machines with multiple read settings that might overlap like assemblers (read recipe & contents) or roboports (read contents & requests).