The photo looks a bit dark; the dress is – BUT OF COURSE – mostly navy. I gave it a wash when it arrived and the white sections came up beautifully. Aaaah, the endurance of pure polyester! The more of these 1960s polyester knits I acquire, the more I believe the story about shops asking manufacturers to stop using the fabric because it never wore out. A quick whizz in the machine with some Persil and it looks as fresh as anything you'd get off the high street today, and I'm pretty sure in about five years time will be looking just as good, unlike those high street equivalents.
Going by the label and style of the dress, I'm guessing this is mid to late 60s. I've seen adverts for St Michael (Marks and Spencer sub-brand) with exactly identical typography on the logo, right down to the placement of the (R) symbol, from that period.