James!...
Solid Shell Slingerland snare drums were NEVER painted with the "chocolate milk" paint... they were left natural. I have a 1968 Slingerland BR/Artist in my Buddy Rich snare drum collection and the interior is indeed natural. That drum was also available in the plied model.. ( more common actually! ) .. and the plied model is painted with the "chocolate milk" paint. Also... there is no reference to a Buddy Rich model snare in the mid/late 60's as Buddy hadn't come aboard with Slingerland yet. He was with them by the Fall of '67 though, so after that, his name was added to the "Artist" model until Slingerland came out with the 4X14 16 lug Buddy Rich Model in late 1969... which was actually cataloged as a 1970.
Tommyp