Treat your "green promotion" as an environmental education program; tell website visitors and guests exactly what you are doing and why. If you are going to the effort of planning and adopting an environmental program, tell people about it! Discuss specifically what you and your staff do for the environment, and don't forget to talk about your charity and community work.
Too often the general public thinks that "going green" means "going without". There are too many four- and five-star/diamond properties around the world that prove otherwise for that old belief to continue. But until hotels start telling people what green actions they have adopted, and guests see how invisible those actions are to their stay, this outdated idea will persist. Tell people not only what you are doing for the environment, but how wonderful their stay with you is going to be.
Being specific about your green actions also helps people sort out whether you are attending to the issues that are important to them, so they can decide whether to give you their business. That's especially true of people with a passion for travelling green, and people with health issues (like allergies). Give people the complete picture.