I see these pale Microtheoris vibicalis quite often, but there are no images of them on BG. I sequenced the COI gene of this specimen along with a dark (typical) one and the sequences are much less than 1% divergent. Here is the resulting phylogenetic tree (the specimen labeled "pale Microtheoris vibicalis (34083701)" is the specimen pictured here).

I hypothesize that the key to distinguishing these is the presence, in M. ophionalis, of a "notch" in the subterminal stripe where it terminates at the midline. Even this pale M. ophionalisone has this "notch".

Here are Microtheoris from CA, OR, WA, ID, MT, AZ in the west and AL, SC, FL in the east (which should omit M. vibicalis)--they all have that "notch". None of the typical M. vibicalis have that "notch".