The boxing glove necklace is one and the same. Period. Whilst all film & TV productions are obviously artificially lit, the lighting director on this show does an exceptional job... that being said:
The lighting in Mike's house is an artificial small side lamp with no exterior light; or even TV (very warm and subdued):
and whilst the El Michoacona restaurant interior is not in direct sunlight, Tuco is sitting front and centre before two huge open panes flooding in scads of Albuquerque ambient sunlight; giving the impression of a more silvery metal:
Head outside, where our combatants are squaring up in the shade, and the gloves are looking more like the prize Mike is admiring as he licks his wounds in the pre-credit post scene:
~ All these tales of Golden Gloves and past glories are pure nonsense. And just because the director doesn't show Mike ripping the charm from Tuco's chest, doesn't indicate proof of there having to be two separate 'Mr.T hand-me-downs'.