Courtesy of the ever-fabulous The Groovy Archives tumblr is this shot from The BIG Tour of 1987-88, and the sartorial choices of YesWest are in keeping with both '80s fashion and their rock star personalities of the time.
I'm actually impressed that they managed such a collective unified color scheme, and also Alan's custom Yes graphic on his outfit is very clever.
Original post:
https://thegroovyarchives.tumblr.com/post/179603098202/yes-live-big-generator-era-via-amazonmusic