In software we leverage some construction terms when we talk about software projects.

Greenfield - a new software project that is not built on a previous project. AKA - blue sky, carte blanche.

Brownfield - a project that is adding onto an existing product. AKA - enhancements, feature work, new version development.

I am going to add to this the idea of Bluefield. This is a project that is a rebuild, from the ground up, of an existing application.

This is very particular to software and I don't know if it has a counterpart in traditional construction.

This project is neither Greenfield (not brand new because it must fulfill requirements of the original system) nor Brownfield (not built on an existing product).

Why are the fields blue?

Let's say that Bluefield projects are akin to the blue sky of a new project (you often have a clean slate on technology), but you can have some sadness about the passing of a tried-and-true system that served you well for some period of time.

Blue is also associated with harmony, faithfulness, and imagination all traits that should be valued in our rebuild project -

Harmony in important features.
Faithfulness to the business intent.
Imagination required to overcome project challenges.