This sweater is really cute as I saw it on fanart. The blonde Eunhyuk made the color brighter. He wore it in Strong Heart.
This sweater is from brand JOYRICHand they called it Neon Ribbed in Multicolor. I think Eunhyuk likes something multicolors for his outfit, and some post about this outfit made him looked a like watermelon lol. It costs $110 but now it's sold out :(