this does make sense!! I have synesthesia and I love to talk about it so :D ty for this question
Hyojin: lots of clear/transparent things in warm colors (dripping honey catching the sun or clear water with ripples), sweet tastes (strawberry usually, unironically), pleasant light linen scent
Changyun: warm oranges and cool greens (partly because of [SECRET REDACTED] and partly just bc he feels very pine forest sunsets to me), rich earthen scents, and a touch of blue when his voice pitches up when his face scrunches up and he gets embarrassed/really smiley
Seungjun: for colors, he's hard to pin down bc he fills a lot; I envision a lot of warm deep reds with his lower register but his higher entertains a cooler bluish end, with no actual distinct purple? which is ironic bc that's his fav color fjsjjf uhh I also associate clear/transparent things with him but more to the effect of cut and polished gems, and not rly any particular scent jumps out at me to him except that when I think of him i get hints of like. warm and slightly musky
Jaeyoung: MEADOWS.. that boy smells like a flower patch to my synesthesia holy shit and clear blue skies color and scent wise, sunny and spring-warm with a light breeze swaying some deciduous trees, JUST before allergens really start kicking asses
Minkyun: predictable maybe but his voice always tastes like a splash of ice cold too-tart homemade lemonade to me, when you come in from the sweltering heat to a blast of aircon in your face and take a sip.. smell wise I don't get much from him either except sun-warmth and? wet skin from either a low chlorine pool or a local lake, but not saltwater
Yuto: he's very Blue and Green to me, brighter and more vibrant spectrums, partly because he makes me so happy and those are my fav colors but also those just jump at me. he makes me think of birdsong and soft giggles about hushed jokes in public, and honestly. no smell conjures from him for me but when I smell bread he occupies my mind fjsjf there's a local bakery I started going to because I love bread and it always makes me think of him when I walk in, it's great