Until I had the opportunity to find these US-made 'triangular' gripping sections, I thought there were few colors that existed. Granted the non-black sections were rare and I was still hunting for the one in midnight blue after I missed an eBay auction in 1998. So besides that midnight blue, the colors I knew about was the burgundy I had. I am also lucky to have a clear or demonstrator section.
So seeing this was a real eye-opener for me! (Mine are the two without nibs.)
From left-to-right the colors are:
Midnight blue, dark blue, light blue
Dark grey, light grey
Burgundy, red, light red
Dark green
Clear
Obviously I omitted the common black section that comes with nearly all US-made 75s.
The most interesting part is that each one of the new colors have the reference zero inscription on the metal ring and also show the distinctive metal band near the barrel. This is the tell-tale sign of being metal threaded sections! All these attributes tell us that these sections were early prototypes, perhaps made even before the 75s were released which dates to a period from1963 to early 1964.