The grey splat ?
I wouldn't be surprised if during production flexing the gauntlet caused a bunch of paint to flake off, so someone in the costume department grabbed a paintbrush to cover up the damage with the closest colour they could find.
I love that he's burst out of his gauntlet in this picture... and has dodgy knees.
THIS is the look I'm aiming for
Irongladiator yes he’s been a huge inspiration and wealth of information.
I was hoping he’d reply as he’s nailed it
Some info can be found here ==> The Empire Strikes Back - Boba Fett's on stage chronology and here ==>ESB main gauntlet damage template.