What you are seeing is a difference in reflectance beween areas which were "tiled" and areas which were not. The nose was tiled up to approximately the line of the cargo bay doors. This can be seen in this pic. http://images.jsc.nasa.gov/lores/S77-28210.jpg
I am of the opinion that the tiled areas were less "glossy" than the non-tiled areas.
Much of the fuselage aft of the cargo bay door line was smooth (untiled). If I recall correctly, portions of the OMS pods were tiled and other parts were not. There are sections of the upper wing surfaces which were tiled (and other sections untiled.
Not too sure what the best colours are to replicate the differences, but you may also consider using gloss/semi/gloss/flat whites to represent the differences.
The aerodynamic tail fairing shown in the post above is white.
(PS: Mike, the NASA T-38's are white with blue trim)