32 C.F.R. § 553.26 – Design of Government-furnished headstones, niche covers, and memorial markers.

(a) Headstones and memorial markers shall be white marble in an upright slab design. Flat-type granite markers may be used, at the Executive Director's discretion, when the terrain or other obstruction precludes use of an upright marble headstone or memorial marker.
(b) Niche covers shall be white marble.
(c) The Executive Director shall approve the design of headstones and memorial markers erected for group burials, consistent with the policies of the Secretary of Veterans Affairs.