I still haven't figured out when they wore the striped off (for the lack of a better expression) blue outfit. On ABBA in concert it seems like they they only wore it for Waterloo. However, since Frida and Agnetha are wearing boots while they were wearing high heels for Dancing Queen, the footage must be from another night. The pic with Björn and Agnetha indicates that they took of the capes (or whatever that was) even before Does Your Mother Know at some points while they kept them on until the very end during other shows.
EDIT: I just saw I posted exactly the same a year ago on the previous page