My Opinion --> ES should protect against all environmental effects that existed in Live, while possibly not protecting against a few select new ones to be added in time. Nullfactor should be about the same, really. Here is where the differences between them are, as i see it:
Environment Shield is targetable, has a cost per application, and a defined duration. Nullfactor Field is more a constant. It has a reactor capacity reduction, and a small buff to recharge rate to even it out, but has a limited range around the Scout ship, in exchange for having no defined duration (instead being a toggle)..
In formations, or close proximity, Nullfactor is more efficient (no "cast time", no remembering to refresh, blankets the whole group in range). In all other applications, such as mining groups who must spread out to make the most of a field, etc...You'd really rather have ES, because it doesn't force everyone to stick together. As more environmental effects find their way into the game over time, each will help more in some cases than the other, so neither becomes favored.
As for ES/Repulsor colors, they worked just like psi-shield did. As you leveled the skill up, the shield would shift tint colors. Max level would have been red, while minimum level would have been blue, with gold-ish being the middle color.