One goal. One world. Multiple brands.
As one of the most influent brands in the world, Coca-Cola is able to head this action and invite other segment's leaders to join this cause. Each participant brand should develop a product line/version following the requirements of the campaign: being green - metaphorically and literally.
The Green Line would be a "cross-brand" initiative, in support of a common need: sustainable consumption.
The whole world already knows what "is" and what "is not" Coca-Cola. By changing one of the brand's element the costumer will still understanding the product and will recognize the new information inputed in this specific line, the marketing over this action would be huge and quickly absorved by the customer.