Use case or problem
I did a little investigation and found out that changing the color of the connection (between two nodes or more, but not all of them) is impossible. That’s sad, because we have the ability to customize nodes colors based on filters, but connections stays default gray (or any other single color). It would be even nicer if there will be the way to set “gradient” color (if connection is between two groups, gradient will be for this two colors).
Proposed solution
I don’t really know how can anybody implement this. Seems like the solution will require a massive code re-writing. But as a feature it would be very nice. This will bring customization to the new level.