Not the same software package, but the Avro RJ has a similar feature.
IIRC the green-white changeover indicates a different source for the information than normal (green = normal), i.e. if air data invalid or unreliable (low speed, on grnd, etc) then the VS display uses inertial velocity (white = alternate).
If memory has failed me, an alternative may be that the air data source has been switched, i.e all on ADC 1 or all on ADC 2. This might also indicate that there would not be any comparator function available for that data.