Stephen is so right with this. In networking we use both terms a lot:
The computer industry loves buzzwords. “Greenfield” is a popular way to describe all-new infrastructure built with no regard for legacy compatibility. But what’s the opposite? Lately, I’ve been hearing companies use the term, “brownfield” to describe a solution that is compatible with existing hardware or software.
I often think as them the other way around. In my view a “brownfield” is a field or even bare land that is not yet deployed, whereas the “greenfield” is where the grass or the crop is growing. The live network thus.