As usual of your flies, a very nicely tied fly.
To answer the question of why McMillan used yellow-olive calf instead of G.P. crest, it was because at the time he originated the fly, he had not learned how to straighten crest feathers or how to tie them in so that they stay on top of the wing. The yellow-olive calf is pretty close to G.P. crest in color and yellow-olive Veniard's dye was readily available for McMillan to use. There is no reason not to use a crest feather as a topping.
Not only does oval tinsel ribbing (usually silver but some flies use gold) over flat silver tinsel look elegant, it serves the very practical purpose of protecting the flat tinsel from getting torn apart; thus the fly lasts longer.
Folks, the torquoise listed in the original pattern recipe is what people on the west coast now call "Kingfisher Blue", and people on the east coast call "Silver Doctor Blue", a bright, light blue. In other words, the exact color that Pastortd used on the fly he pictured.