"White" and "Red" bug speeds are determined from the charts dependent on take off weight.
Typically for the ATR 72 at, say, 20 tonnes the speeds are:
White Bug = 134 Knots
Red Bug = 161 Knots
Also from bits and pieces of CVR in the media:
Sounds like they never got to "red bug" - I figure this means they retracted flaps too soon for the icing conditions?
Decoding starts from the moment when the commander turns on autopilot and removes the flaps. After that the ship starts to shake, and the commander takes control, but the plane lurches - first right, then left, losing altitude and falls. Report to ATC, neither the commander nor the copilot have time.
Voice informer: Autopilot on. White Bug
Pilot 1: What is that shaking?
Voice informer: Autopilot disengage.
Pilot 2: Silence!
Pilot 1: What is it? Report!
Voice informer: Don't sink.
Pilot 2: What's to report? What's kind of failure?
Voice informer: Don't sink.
Pilot 1: UTair 120 we are falling