The following charts and pictures on the dating bottles pages listed below should help.
Of all the bottle collecting categories, bitters bottles are among the top. This is because bitters collectors like the wide variety, the interesting forms, the wide range of colors and their historical significance as a uniquely American 19 century fad.
) bottle (the Turner Brothers barrels are really Eastern items).
These used to be virtually unobtainable and rarely seen, though due to a couple small caches of them being found some years back (Nevada & Oregon reportedly) there are a few around now...including this excellent example.
(If you are looking for one of these you likely know the stories better than I.) These bottles date from only 1869 according to Wichmann's great "Antique Western Bitters Bottles" book (and the Wilson's 1969 classic) who listed them as valued at "$3000 to $7000" in the various shades of amber (the unique light citron green example was unknown at that time).