From my many days (and semi current) as an artist, I have learned that most
pigments are actually a concoction of many different pigments. Black has the
most involved. You can see this when you put a strip of water based black
marker on chromatography paper and put it in water. Black is actually a
combination (in color theory not light) of all colors of the spectrum, whereas
white (this again is color theory not light) has no pigment. I have learned
that when extreme amounts of pigments such as reds, greens, blues or purples
are present, that they will appear black. I just took a very close look at my
marmosum and here is my analysis of the color: The deep black/brown looks to
be a concoction of very high levels of purple and yellow (for those non
artists, these are what is known as complementary colors because the are
opposites on the color wheel and they "compliment" each other). Of course I am
looking at it under a 75watt light bulb that gives off higher levels of yellow
light.  I would try to match this color but at the moment I am out of yellow
paint (I prefer clay to paint anyway) The color of the ranius, I am imagining
to be, sounds like the color of a very high concentrated Iodine solution. It
appears black, but in actuality (when put under a spectrophotometer) is in the
middle of red/orange with what looks like a little purple and green thrown in.
         True black is actually a very rare color in nature. I frankly don't believe
that animals (or other organisms) produce black pigments because of the shear
number of pigments involved, they just look like they do because they contain
such large amounts of other pigments.  I would love to read or hear more about
the pigments that are involved.
Again, just another of my two cents
Sarah
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