In my experience, building on MSW of any kind has been a failure in the long term, developing excessive waviness over a period of years. Obviously, it is diificult to characterize bearing strengths of MSW. In fact, I've seen some roadways repaired to correct this problem only to develop it again...
I assume you mean black on both sides, to keep red-phase drivers from anticipating a change from reflections off the illuminated signal? That's a good idea, esp. with all the bright LEDs going in, but I've never seen it in Ohio where I am.
