Clearly it makes sense to communicate your organisation's green product attributes and environmental achievements, but greenwash should be avoided at all costs. Finding the right balance can be tricky, and the consequences of getting it wrong can be catastrophic. Green marketing is a still an emerging discipline, so it's a bit of a moving target, but here are some guidelines:
Be authentic - don't invent a green benefit for your product where none really exists, or exaggerate your claims.
Be transparent - the more data you can provide to support an environmental claim, the more credible it will be.
Act first, tell later - don't boast about an environmental achievement before it is delivered - but feel free to share targets and let your stakeholders know when you have achieved them.
Get endorsement - having your claims or achievements independently verified can add greatly to their credibility.
Keep up to date - your competitors are greening their products too, so the status quo is constantly changing. Your products and services will need to evolve with the market, and so will your messages.