Unable to live another second without an answer, I called Montana and spoke
to a 'known to be bugwise" person. I was told that the color is related to
how old the bug is AS a spinner. In other words, when a PMD dun molts into
a spinner it will be the olive cast, but it darkens fairly quickly, and gets
darker until it falls.

This seems to fit other 'facts" I have, such as it is my "impression" that
morning PMD spinner falls have a majority of olive colored spinners, while
the evening falls seem to have a much higher percentage of rusty ones.
This is just impression, thinking back on days I remember, I've never really
counted but I do usually glance at the water and start with the color that
seems to be most available.

--------------

There is nothing original here, but while I'm typing ( and I've been tying
these which is what got my poor old brain pointed this direction ) here is a
nice "Last Light Spinner"

hook ... 100 BL ... 16, 18 ( 18 mainly for where I fish )
thread 8/0 ... rust
Tail ... dun microfibits (sp) or some such .. a little long
body .. rusty turkey biot tied smooth ( house of Harrop has high quality
biots in great colors ... I 'think' Harry Mason sells them )
parachute post ... flourescent orange poly post ... trimmed a little shorter
than you want to G... it's an indicator, not a wing
lower wing ... half dozen fibers of sparkle organza tied spent, just behind
of post and trimmed to wing lenght on each side ( optional, but a nice
touch )
thorax .. fine dubbing, rust color
parachute hackle wing ... white, the barbs roughly the length of hook
shank , trim away the part that comes out over the head, so only barbs
coming out the sides are left
liquids ... head cement if you are so inclined and WaterShed, for sure

easy to see most of the time, compared to other spinner ties, and fish eat
it