There are about two dozen nice color photos of S. alatus variations in a
little book by Harlan Wittkopf, "The Sanibel Kaleidoscope", pp.23-27.
Figs. 94-94 on page 54 also show four different aperture colors.
Furthermore, there are photos of juvenile and aberrant shells at
figs.99,101,102, and 108.
Winston Barney
Fort Worth, TX