The First Prototype Boba Fett costume is often referred to as the Preproduction #1 costume, prepo 1 costume, or simply PP1 costume.
These photos show the First Prototype Costume being fitted to an actor, piece by piece.
This costume was supposedly painted by Joe Johnston after the decision was made to move away from the all white "Supertrooper" style of costume.
The helmet which accompanies this costume is often referred to as the "Eyes" or "Ears" helmet due to the eye-shaped markings on the top of the helmet.
Note that the eye-shaped marking were moved from the front of the dome of the helmet to the top of the helmet. Faint lines can still be seen on the helmet where the markings were originally located.
This costume was eventually sent to Sandy Dhuyvetter as a template which she loosely followed to paint three additional costumes.