Ruiz and Pereira recently lamented the “arbitrary naming” to describe color in rock art, such as “wine-coloured red.” They also viewed the scales (including IFRAO’s) and charts used by rock art researchers as limitations and at an impasse. 
Why is this important? Well, they say, to create better understanding and to assist preservation. All for the good.
Still, as the science of color in rock art inevitably advances with digital technology, it seems to me this is a sweetly fitting moment to recall Heizer and Baumhoff’s 1962 call for further research in “determining the importance of chocolate –colored basalt in providing proper surfaces for inscribing petroglyphs.” This basalt was, in their opinion, an ideal material. 
Plew described a similar distribution pattern in SW Idaho. Many petroglyphs occurred in areas where chocolate-colored basalt was available and where it was “limited or absent, few petroglyphs occurred.” 
So, may I offer – as an album of boulders from a Lake County rim - an indulgence of petroglyphs on richly-patinaed, chocolate-colored basalt? Best viewed with a cup of wine-coloured refreshment in hand. All with fond remembrance to the subjectivity of “human differences/acumen in identifying colour.” 
 Juan F. Ruiz and José Pereira. 2014. The colours of rock art. Analysis of colour recording and communication systems in rock art research. Journal of Archaeological Science. Vol 50 (Oct 2014): 338–349.
The authors propose, “a reliable solution for recording of the colours of rock art, ” with the aim to “ produce an objective description of colour are essential to describe rock art colour in an accurate and reproducible way, even in complex recording environments such as open-air rock art sites. Human differences/acumen in identifying colour will always lead to subjective and potentially non-repeatable identification in the field.” (348) Pereira’s Digital Heritage website offers a rich portal into this realm: www.jpereira.net
 Robert Heizer and Martin Baumhoff. 1962. Prehistoric Rock Art of Nevada and Eastern California. University of California Press, Berkeley. Of course, the term “chocolate–colored basalt” did not originate with H&B, though it’s likely they first applied it to rock art. Indeed, the San Francisco Theological Seminary, built in the 1890s just across the Bay from Berkeley, was constructed of “stone of a chocolate-colored basalt.” SFTS remains a distinctive 14-acre complex and is a favored setting for weddings.
 Mark G. Plew. 1996. "Distribution of Rock Art Elements and Styles at Three Localities in the Southcentral Owyhee Uplands". Idaho Archaeologist, 19(1), 3-10.