Yes, it’s summer in San Francisco. And by “summer,” we mean it’s damn cold and foggy at night.Keep extremities protected with a lightweight Venn Apparel scarf, made from soft Japanese wild silk. Local designer Zara Franks named the company not for the math diagram, but for her great grandmother, Ethel Venn, an English emigre who ran a tailoring atelier after arriving in the U.S. in the mid-1800s.The hand-dyed scarves come in four styles: We like the traditional Drape and the more modern, circular Loop. For summer, the mostly white scarves get splashes of color inspired by stormy skies and American landscapes (think navy, mustard, lavender-gray, and cranberry).Franks is planning a few ready-to-wear pieces for fall, including an embellished alpaca sweaterdress. Which we wouldn’t mind wearing tonight.Available at Button Down, 3415 Sacramento Street, at Walnut Street (415-563-1311); online at vennapparel.com, $112-$175.Photo: Courtesy of Mathew NellenGoing somewhere warm? Take a peep at our swimsuit gallery.