The blueprint gets its name from the cyanotype process, invented by John Herschel in 1842. The process used a photosensitive solution of ferric ammonium citrate and potassium ferricyanide, which turned Prussian blue when exposed to UV light. Unexposed areas, blocked by the original drawing on translucent paper, remained white. The result: white lines on a deep blue background.
For over a century, blueprints were the standard method for reproducing architectural and engineering drawings. They were cheap, durable, and infinitely reproducible. The format became so iconic that "blueprint" became a metaphor for any detailed plan — a blueprint for success, a blueprint for reform.
On the web, the blueprint aesthetic strips away ornamentation and replaces it with precision. It says: this was engineered, not decorated. The grid lines, dimension marks, and monospace type all communicate competence and intentionality. It appeals to people who find beauty in technical drawings — who see a well-dimensioned floor plan as more elegant than any watercolor.