You can create a two tone border within the same (non-group shape!)

[wapperdude]

This would not work, in general, for randomly shaped 1D shapes.  There are cases that it does.  Connectors, with their auto-rerouting would be particularly troublesome.   Likewise, 1D shapes with interior steps / jogs would not behave well.

As Yacine states, don't give up those custom line patterns!

[hidden layer]

Looks cool. But can you do it for a connector, i.e. make a two-colored connector, or a striped one?
Without using the line patterns?

I did this but WITH a custom line pattern. I have few of them e.g. gn/ye. I tried to have access to the colors but I didnt got it

But its interesting... if not exciting