I've used those hinges without a problem. It's a good idea to flex them around the hinge line before you install them, just to 'break them in'. I used four of them on each aileron of a Sig LT-40 with no problems. I didn't pin them, just used epoxy in the holes. Dry fit them first to check the position.

As for how white over blue on the monokote, I believe that monokote recommends that you put the dark color over the lighter one or else it will definitely show through - I know that this doesn't answer your 'how badly will it show' question, but thought that I would mention it.

Hope that this helps.

Bob