I feel bad- a lot of the small bladders that hitch-hiked in on my plants have clear shells and I know it's because of a lack of hardness in my water. (MTS seem fine though)
I'm adding some buffer tonight- so hopefully that will help the poor fellas out.
Incidentally- the red ramshorn is red (from what I've read) because it has red blood (unusual in snails) and has a very thin partially transparant shell. The colour of the snail inside the shell helps colour the shell... or something like that.
Anyhow- I only say that because- if that's true- it must mean that ramshorns have thin shells- and yes, quite likely some can be transparant.
Also- I've read ramshorns are some of the most affected by low calcium and low pH... so it could just be an unhealthy shell too...