NEW YORK — They were splashy and fun in the Sixties, and this season, Marimekko prints are back. The renaissance of the Finnish textile firm’s designs started in home furnishings not long ago, and then the bright, childlike patterns turned up in a handful of sportswear collections for spring. Now, it’s swimwear’s turn, as designers use them for the season’s hot shape: the one-piece. Here, a nylon and Lycra spandex suit from La Blanca by Rod Beattie. For more, see pages 4 and 5.