TL;DR
All we need to have for distict power networks is power poles with different colors and a tool to change that color. No need to produce new items, just use the tool to change it.What?
See the orginal suggestion viewtopic.php?f=6&t=70996 Control Power Connections by Coloring Power Poles (with Lamps)I thought of this all and due to this thread I came back.
Thanks for the input. I think using colored wires for power is really not the best idea. Colored wires have a basic problem: You don't see them very well, especially when you look in max zoom out onto it. But that's an important view for doing such things. I think everything can be made much easier, if we have colored poles.
This is the idea
We have this types of poles: Normal, pink and blue (for example to mix them not up with red and green wires). Each color is an identical set of poles from the "normal" color.
The player cannot place these new poles. He/she needs not to produce the pink and blue poles! Instead the player has a tool with which she/he can change the colors of the poles between these three colors.
In the moment of color change per pole remove all connections to/from this pole (and also all poles in reach, but not connections to power switches) and rebuild the connections without connecting poles of different color. All in one tick. To bring the game not to stuck when drawing big areas with many poles, only one pole per tick is really changing color. Gives a nice effect.

So this tool can also be used as a wanted side-effect to redraw all electric connections (normal to normal) in an area to have nice looking electric connections.
On blueprint placement normal poles can be used and they change color when placed. On destruction the poles change the color back to normal, so the player will never have to hassle around with more items than now.
That's it. No complicated placing of lamps etc.
And - AFAIK - can be implemented as a mod. The mod needs this:
- on initialisation create the other poles (pink and blue). (Hm. I think the poles have no tint to change the colors. How about placing a colored think on top of the pole to show the color? A lamp for example, with no surround shine)
- The tool to select the area of change
- A kind of menu to change the color in which the tool will change for the next time
--- Every selected pole comes into a queue
--- The queue is emptied one piece per tick with the above described algorithm.