The more you think about this, the more uncertain you become. Most jobs can be greened or at least greenwashed; in Portland, for example, there is a vegan strip club. On the other hand, you could make a Malthusian argument that no job is green because anything that creates value for people helps them and facilitates their attrition campaign against the earth.
How to define green jobs may not seem like a pressing concern, but it does matter, because the parameters of the population determine its observable characteristics. That in turn will impact our views about green jobs and our interest, or lack thereof, in trying to create them.