Vne is a required marking on the airspeed indicator and airspeed indicator markings show indicted airspeed. Besides, the things Vne is based on (flutter, etc.) are dependent on indicated airspeed.
US FAA aircraft certification guidance
§ 23.1545 Airspeed indicator.
(a) Each airspeed indicator must be marked as specified in paragraph (b) of this section, with the marks located at the corresponding indicated airspeeds.