See page(s) 35-115 and 35-116 of the G3X Touch Installation Manual (Garmin Part # 190-01115-01 Rev. AM). i.e.:
"For certain aircraft types, maximum airspeed is additionally limited by true airspeed (TAS). A secondary
airspeed limit expressed as true airspeed may optionally be configured using the VNE - True field. This
airspeed is marked on the PFD airspeed tape with a second red color band, which shows the equivalent
indicated airspeed at which the aircraft's true airspeed will exceed the configured true airspeed limit value.
At low altitudes where true and indicated airspeed are similar, the PFD airspeed tape will show only the
indicated VNE limit. At higher altitudes where true airspeed increases, a second red color band will begin
to appear on the PFD airspeed tape to indicate the point where the aircraft will exceed the true airspeed
limit at the current pressure altitude."