Here we go, from my post on Devil 505's thread:
It's part of Spec 98-24105-P, information available here:
http://librarum.org/book/31199/37"Their markings were to conform to Spec 98-24105-P and amendments, except that the marking 'U.S. Army' on the under surface of the wing was to be applied with blue, Shade 47 of Bulletin No. 41. All other exterior markings were to be applied with either red, black or blue, Shades 45, 44 and 47 of Bulletin No. 41."
Shade 47 is the same as ANA605 Insignia Blue per Bulletin No. 157.
So yeah, the U.S. Army stencil should be the same color blue as the roundel.