My recently installed BS66-basically Swing Bass just as well-were gray/dull looking in the new package (have used them before in the older packaging as well.) Forgot if before they were shinier, but definitely much duller than the stock nickel plated strings of a new bass they replaced, which were less deep sounding and much thinner. Because of the still excellent mids, definitely very clear strings, very colorful and "alive,", which are their main strength in my view. Not sure if the "brightest", but certainly very "there".
I tried heavy Slinkys briefly few months ago on another (failed) bass, and it could have been the instrument-not so sure-but they sounded more average "good" than the Rotos, though of course they are well-regarded. I can no longer use them because I cut them for a different, L/L, R/R headstock, but do not miss them too much, despite them being "new". Rather keep using these BS66s for this particular bass-awesome thunder, clarity, and a great, great E tone.
Cannot comment on the 70s/80s/90s, sadly. Just think they are sounding great today, even compared to other more modern brands.