The term Eco actually has multiple meanings depending on the usage:
Ecological can be the root which means interactions of organisms on earth to one another and to the environment. To put it simply, how people, animals and the planet coexist. Often this comes from the school of thought that humans are at the top of the food chain and are meant to be stewards of the living planet. Humans protect it and have dominion over what lives and dies.
Eco can also mean Economical which means affordable, inexpensive, low-cost, budget, prudent, thrifty.
Sustainability is the capacity to endure. It is the endurance of a system or process. Sustainability is becoming an increasingly popular concept to discuss the viability of well… EVERYTHING. You can talk about sustainability in regards to a relationship, a business or a conversation of ecology.
If Ecology is how people, animals and the planet coexist, sustainability is a measure in time of the long term viability of those relationships.
If Economics is people in relationship to commerce/money, Sustainability is a measure in time of how long the current relationship can continue to exist as is and yield value.
Green is most obviously the color which is a combination of blue and yellow on a spectrum of visual light. Metaphysics would say it is the combination of Water (BLUE) and Sun (YELLOW) which makes the plants and green earth around us. Both would be correct.
In this context, green is referring to an ideology that acknowledges people as stewards of the planet. It is also a term used to identify a group of human beings and a movement. The Green Jobs movement, for example, is about moving humans away from thinking of ourselves as white collar or blue collar. Green collar is the future. It is for people who want abundance and to live lives of purpose. Unlike white collar and blue collar that were designed for people, Green collar gives the workforce some autonomy.
Green focuses on creating win, win, win scenarios for all involved. The green collar movement takes into account long-term viability (sustainability), human needs, and the environment in order to create lasting abundance.