(a) Except for size and color, the square background required by §172.510(a)
for certain placards on rail cars, and §172.507 for placards on motor vehicles
containing a package of highway route controlled quantity radioactive materials,
must be as follows:
(b) In addition to meeting the requirements of §172.519 for minimum
durability and strength, the square background must consist of a white square
measuring 14 [Amdt. 172-29, 41 FR 15996, Apr. 15, 1976, as amended by Amdt. 172-64,
46 FR 5316, Jan. 19, 1981; Amdt. 172-78, 48 FR 10226, Mar. 10,
1983]