As the third and final economic policy option, Green completes the triad begun by Free market and Planned. It is worth noting that the first two options are found in chapter 2, at an earlier stage of colonial evolution. This comes down to two factors. First, both free markets and planned economies have precedents on Earth, and are thus readily available for local adaptations as soon as the infrastructure is in place. Second, while there are ecological schools of thought available to us at present, they are (by virtue of our being on planet Earth) not developed with a radically alien ecology in mind. For an economic system to be green, it has to be based on a firm understanding on the ecology it finds itself in. This understanding only manifested itself after the attainment of Centauri empathy. It is, as a popular cultural icon once noted, not easy being green.
As with the other social choices, Green does not represent a single fixed ideology, but has to be read in conjunction with the other choices made. The differences between a green fundamentalist faction (the Cultists spring to mind) and a green police state are not subtle, and neither can be confused with the economically optimized (an Efficiency rating of +4 is not to be trifled with) combination of a green democracy. The stark differences aside, what unites them all is an informed decision to make every effort possible to not disturb the local ecology more than absolutely necessary.
The commitment to not cause ecological damage is, at its core, a scientific endeavor. Although motivated by ideology, it takes quite a bit of empirical observation to determine whether one action or another has actually made an impact or not. Ecological cycles are slow, complex and encompass vast ranges of territory, meaning that a local mindset simply will not do. Monitoring the ecology requires extensive infrastructure of sensors, monitoring stations, and institutions to go through all the collected data. Said data then has to be used when making decisions as to what to build, where, at what scale and (in ecological terms) at what cost. This data-driven economy is a very different beast indeed compared to a profit-driven alternative.
The benefits of this mode of economic governance are obvious. Once the data is collected and assimilated, making good decisions becomes second nature (or, at least, not making atrociously bad decisions). It does, however, take quite a while to get into the mindset (individual and collective) that enables this mode of social organization to come into being. A person is not born as an environmental analyst, but is made into one. The individual and social learning curve involved with implementing a green economy is steep, and thus there is an inherent risk of developing into a technocratic mode of governance where only those steeped in the intricacies of ecological processes are able to form useful and actionable opinions on further economic development. Being ecologically sensitive does not preclude the potential to perpetuate a class society; indeed, it is arguably better at it than the alternatives.