From the Tech Manual...
"The trunk of M-B´s in the 60's (like W113) is actually not black, but a very dark gray. It can be ordered via Mercedes dealerships. Ordering code is 000 986 67 33 - 7164. The "000 986 67 33" is the part number of a one component (not catalyzed) paint sold by MBAG, and the "7164" is the color code for this deep dark gray. It is semi-gloss."
My 1966 built 230SL "survivor" (original red tire pressure label and hang tag) is definitely "very dark grey" in the trunk.
Kevin