Commercial blueprints for at least the last twenty-some years have been diazotypes. Different sensitizers precoated on paper in large sheets for blueprint and blueline, and developed by exposure to anhydrous ammonia. They are not cyanotypes, though blueprints originally were.
Traditional cyanotype is a negative process -- light exposure turns the sensitizer blue -- but there is a direct positive version, using ferrOcyanide instead of ferrIcyanide. This starts blue and turns light, then washes away, where exposed to light (I think, I've never used the positive version; I've only needed to make cyanotypes from photographic negatives).