Wilson was a member of the group from its start as a group of Chicago neighborhood girlfriends, who made their first costumes with skills learned at school home-ec classes. (I wish one of those dresses had been part of the exhibit!) The gowns on display come from a bit later in the Supremes' career, including couture by famous designers like Bob Mackie.
Overall, the effect is of fabulous '60s and '70s glamour. "Fabulous" is the word. The lines of the gowns are usually simple, lean, even severe, but the materials are rich and often heavily encrusted with beads or sequins and the colors strong, so that even on a mannequin they seem to want to shimmy and shimmer... These aren't evening gowns - though that's the look - but performance costumes. They want to move! I wish there were video clips to show this fashion in action.
Photo borrowed from The Supremes Lyrics
And here's a video clip on You Tube: The Supremes at the Hollywood palace