Hi there and thanks for your informative site
As best as I can see – the moths on my front porch today are Modest Sphinxes – they do not seem to have the distinct battle colors of the Cerisy’s. We live in the country east of Parker Colorado
Your photo is breathtakingly beautiful. This is a species closely related to the Modest Sphinx. It is the Big Poplar Sphinx, Pachysphinx occidentalis, the pale color form. Bill Oehlke’s wonderful website has some nice images of this beautiful moth. We have also heard it called the Western Poplar Sphinx.
Update: November 29, 2015
Bill Oehlke Responds to comment.
My guess is they are both occidentalis, based primarily on the basal area of the forewing, but they could also be both modesta or a male modesta with a female occidentalis, but first choice is both are occidentalis.
Thanks for thinking of me. Please see if I can get permission to post this, credited to photographer (name??) to a Douglas County pictoral checklist that I would create.