RR Urban wrote:

When it comes to AIRCRAFT visibility, who can point to appropriate
research recommending orange as an OUTSTANDING color?

I can't point you to research regarding a specific color,
but I can tell you that someone, Keith Ferris (the artist)
ISTR, has lectured on color and spotting.

What might its value be for exceptionally small aircraft approaching
head on in bright light with closure rates of nearly 400 mph?

At these closure rates and times and considering you're not
always staring directly at the target in question the differences
in colors are probably minimal.

Dave 'glint' Hyde