PLAINS, GEORGIA — When Jimmy Carter chose branding designs for his presidential campaign, he passed on the usual red, white and blue. He wanted green. Emphasizing how much the Georgia Democrat enjoyed nature and prioritized environmental policy, the color became ubiquitous. On buttons, bumper stickers, brochures, the sign rechristening the old Plains train depot as his campaign headquarters. Even the hometown Election Night party. “The minute it was announced, we all had the shirts to put on — and they were green, too,” said LeAnne Smith, Carter’s niece, recalling the 1976 victory celebration. Nearly a half-century later, environmental advocates are