Mary, the first thing I would point out is that Flinties aren't clear.
The earliest flinties looked practically transparent when you held them to a light, but they were still translucent.
Something which may not be known is that not all flinties had the fish eyes.
The earliest, most nearly clear flinties did not have eyes. (unless I am mistaken both in what I have read and in the name of one of my early flint-colored akros)
As they became less translucent, some got eyes.
There are even virtually opaque flinties, but you can see the orange glow through them if they do have the fish eyes.
Without the eyes, the most nearly opaque ones may be indistinguishable from other companies' game marbles but the ones which are closest to being clear still stand out.
Here are some photos of Flinties and Moonies in original packaging.
Box 1:
Box 2:
Box 3: