A blueprint is an in game item that you must posess in order to craft an item. Each blueprint is for the creation of a specific item, and also tells you what materials are needed to create that item. Blueprints must be inside Blueprint Books to be used. Some of the low-end lvl-1 blueprints can be purchased from the technician, others can only be gained by buying from another player, or are discovered while crafting other items.
And no, blueprints are not blue, they are called that because in the real world the old mimeograph machines printed in blue ink. Ok, I don’t really know why, that’s just my guess. Go google it if you care.

Why Blueprints are blue (Or at least why they used to be). Modern equivalents, sometimes incorrectly called blueprints, are more accurately ‘Blue lines’ or whiteprints. Yes, apparently I DO have way too much time on my hands… :)