Posted by scvirginia (Charleston, SC - Zone 9a) on Jun 15, 2020 9:54 AM concerning plant:
Description from the May 1937 Bulletin of the American Iris Society, p.25:
S. de Vlieger—S[tandards] Pallid Blue Violet deepening at the base toward Pale Bluish Violet. Style branches same as S[tandards]. F[alls] almost white, barely flushed with Pale Mazarine Blue so that they look faintly gray.