[Byron]

Some good pics there - and I would even go back a little
earlier with dates.

It was possible to find what Brazilians would call tangas in conservative "gentlemen's outfitters" - such daring beach
and swim briefs* would not be seen there today.

Fast-moving fabric techonology had its influence on styles
and colors of course and speedos were only part of a new
fashion trend that encouraged the wearing as leisurewear
of athletic clothing only previously attributable to a particular
sport (just see the profitable paraphenalia for sale in soccer
club shops).

Winston Churchill's romper suit of WWII became the new and
(sometimes horribly) colored shell suit or track suit to be worn
to the shopping mall for example.

* terminology has changed - to say swimbriefs meant precisely
that and was an alternative to "swimming trunks".
I have learned from much earlier confused searching on the internet
however that briefs in the USA means underpants (but, just to make
things even more confusing, trousers are pants).