It's a flippy fad!
Sonic gets to follow a fad here with this tee. "Flip Up Sequins" are a fad on shirts for kids (or probably anyone--but it's mostly for kids) in 2020 and 2021. Probably 2019 started it. With this gimmick, sequins are sewn onto the shirt in a special way that they can all lay like fish scales. However, since they're fastened in the middle, they can be brushed at with a hand and made to lay the opposite way, revealing the color on the other side of the sequin. In this case, it's a bronzy gold on one side and on the other they're metallic reddish. By setting the sequins into the 'lense' area of the sunglasses, you can choose how they look for classic Sonic.
They use forward-facing Sonic from the waist up for the stock art here & have his name spelled in a block/comic book type font below.
ANY item featuring such sequins should only be washed by hand, not in the washer.
This shirt, as it has a gimmick may cost a bit more than usual at 12 or 13 instead of Target's usual 9 or so for a kids/teens tee. This is a 2021 Target / winter item.