The colors don't mean anything outside of a range of dates and data. It's red because around this time, it's usually faster, but when the rate suddenly changes, all Google informs you of is that change. That's why a road that's fairly slow will be green if it's normally slow. People are driving slower because you're supposed to; even speed limits are for maximal conditions (sun, clear skies, no precipitation).

You'd have to be a dipshit even by MA standards to try and push it when weather conditions are worse and changing right in front of you.