14 CFR 27.1545 - 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.
(b) The following markings must be made:
(1) A red radial line -
(i) For rotocraft other than helicopters, at VNE; and
(ii) For helicopters at VNE (power-on).
(2) A red cross-hatched radial line at VNE (power-off) for helicopters, if VNE (power-off) is less than VNE (power-on).
(3) For the caution range, a yellow arc.
(4) For the safe operating range, a green arc.