The picture, below, contains Parker pens from the 1930's including the Parker Vacumatic and Parker Duofold.
All feature what is known to collectors as the Jeweler's Band- a wide
capband with concentric banding, and a cartouche
for optional engraving.
The Jeweler's Band pens can be found in high line Vacumatic pens from 1939-41 in four sizes and apparently in but four colors
Junior line shadow wave pattern Vacs can be found in three colors and in two sizes.
Pens from the 1940's Duofold series (usually characterized by striped
color patterns) see the Jeweler Band appear
on otherwise low-line button-fill pens, in two sizes and four colors,
produced this way from 1940-1, perhaps through
early 1942
The Jeweler's Band does crop up in the 1939 (perhaps through early 1940)
so-called "Toothbush" Duofold series, as well.
Appearing in both sizes of pen, it probably can be found in all four
colors.
Concrete history regarding the niche filled by pens with the Jeweler's
Band remains unavailable, to the best of this writer's awareness,
though speculation abounds.
neat pens.