Is the number of skittles in the image correct? You don't otherwise provide how many are being poured. Or do you want a general solution for arbitrary N?

I don't see how this is possible. Theoretically the random scale has a small possibility of replicating either of the constant scales indefinitely just by random chance. If it randomly gives the correct answer the first ten times, any observation on it will be the same as if it were the truth telling scale; same with if it's a hundred or infinite times.