It works, but trouble is that you really need the whole length to see the markings. Either way though I'd not worry too much if he seems healthy and is eating. You can always get more sand sifting snails if you are concerned about stirring the substrate.
I did note that and I was aware of the idea, but as I said, it is not 100% supported and doesn't have enough evidence behind it (yet). No histological studies on multiple specimens have been done to prove it so far. Not to mention that it doesn't explain why there are occasional yellow-yellow pairings.