starwars.com updated with new info about the origins of Boba Fett.
starwars.com: Proto Fett: The Birth of Boba
According to Empire's "making of" book, Once Upon a Galaxy, Boba Fett's character had originally emerged from that of Darth Vader:
"I wanted to develop an essentially evil, very frightening character," said Lucas of Vader. "He started as a kind of intergalactic bounty hunter, evolved into a grotesque knight, and as I got deeper into the knight ethos he became more a dark warrior than a mercenary... I split him up and it was from the early concept of Darth Vader as a bounty hunter that Boba Fett came."
Born of Vader, Fett required an equally villainous look, but something a bit less conspicuous. Designing Fett's signature helmet, armor, and accoutrements fell primarily to Joe Johnston, who worked in tandem with Ralph McQuarrie to come up with the bounty hunter's distinctive look. Far removed from the black-on-black wardrobe of Vader, early concepts for Fett clad the bounty hunter in white, possibly a vestige of his "Super Trooper" origins. This all-white Fett was actually the first costume produced for the character, officially unveiled to Lucasfilm insiders in a screen test shot on June 28, 1978.
starwars.com Picture Viewer of Boba Fett's screen-test footage:
[web]http://www.starwars.com/episode-v/bts/article/f20061019/20061019_picview/pictureviewer.html?imgNum=1&world=episode-v[/web]