I have the same request. If anything, any chance to add (sorry, i really do NOT know how to help) where we can set the value for the colour? (you know how we do for character and train). Since like that, we can ajust more or less.
Also, i don't get it. Are people using so many gates that the issue matters? Usually i have it for trains. I mean, if I want to move my (non flying) character pass a solid wall, i only need to temporary mark them for deconstruction (just that, marked) and i can pass, and them undo the marking (aka no bots needed).
And otherwise, i don't know any reason to mix the walls unless you are short on materials or something