Original: Persian blue ( not to be confused with prussian blue ) comes in three major tones : Persian blue proper -- a bright medium blue ; medium Persian blue ( a medium slightly grayish blue that is slightly indigoish ) ; and a kind of dark blue that is much closer to the web color indigo ; this darker shade of Persian blue is referred to as Persian indigo , dark Persian blue .
Simplified: The source of this color is a color sample taken directly from a photograph of the Persian blue tiles on the interior tile work of the dome of the Shah Mosque in Isfahan , Iran .