The answer to the blank space is green marketing.
The Prius is supposed to be marketed for its great value and environmental benefits – thus making the type of marketing the company is doing a green marketing. A green marketing is defined as the process of marketing a product or service based on their environmental benefits – it could be because the product itself is environmentally-friendly (such as the Prius, which is a hybrid electric-gasoline car, which means that it won’t emit as much pollution) or because it is produced in an environmental-friendly way.