Late entry in the sweepstakes --

"earth color:  a colored mineral (as an ocher) used as a pigment."
From: Webster's Third New International Dictionary (Unabridged), 1963.

Though this predates the 1970s definitions, it doesn't use the word "tone."
Good because it is so concise.  Doesn't leave much room for interpretation.
Implies that the coloring substance is all natural (could have been refined, but
not subjected to chemical alteration).  Can ya dig it?    ; )

BPopkin