The fly is upside-down in this picture. Hind femur at left, mid femur at right, calypter at bottom of picture.

Whitworth's key to blow flies(1) asks for the color of the "lappets of posterior thoracic spiracle." Is that the dull orange spot just above center, partially covered by the leg?

Choices are "dark brown" and "pale yellow to orange." Unfortunately the latter choice, which looks right, leads to a contradiction.