Do you go to the farmers market looking for a specific ingredient? Or do you go and see what sparks your interest? What you’re making for dinner can of course lead the way, but this week at the Provincetown Farmers Market something stands out: the great variety of purple vegetables. Brightside Greens has long, thin, deep-purple-skinned eggplants, purple pole beans, and purple broccolini, all grown in Truro by Eric Loscher. Down Home Farm, run by Digree, Bhala, and David Rai is a Truro favorite. They have beefy lavender-hued eggplants, purple cabbage, and purple bunching onions. Dinner this week? Purple.