This picture from Entertainment Weekly says that this is the Bee Gees in their heyday, but,sadly, this turned out to be a dark spot in that day (Note the silver "Balloon Chase" uniforms they're wearing - why does EW even mention Fever and show this picture!) - they were on their way out, with "Spirits Having Flown" as their swan song. Popularity would elude them until the late '90's, with a successful album and tour.
Take a close look at the shirts the Bee Gee's and Peter Frampton are wearing when they start to sing "GETTING BETTER." After the Mr. Mustard intro. scene the film goes back to the band singing, now look and see that their shirts have changed! Maurice Gibb's T-shirt has changed into a button down shirt, and Robin's green shirt has changed colors from green to white with red stripes. Did they change shirts during the song? Is it supposed to take place on another day? Strawberry Field's clothes are still the same. One fan offered that they apparently were recording over a period of days, with the change of clothes happening over a montage. That has to be it.
Accidental nudity alert! while the LHCB are in the studio, Dianne Steinberg leans forward to reveal that she isn't wearing a bra under her loose-fitting outfit. You heard it here first, guys!
During the "orgy" scene, the signatures on the contract look totally different from one shot to the next. [Especially when the contract is blown up for the "I Want You" halucinating scene on the record-shaped waterbed].
Mr. Blevins has a great point here: "If Lucy and the Diamonds are so successful (they have something like three hits in the Top 10 [as far as the film is concerned]), why does Lucy have to be B. D.'s chauffeur , photographer, [hostess, and whatever else]? What kind of contract did she sign, anyway?"