On Thu, 8 Apr 2004 23:51:29 +0000 (UTC), Tim Tyler 
wrote:

>r norman  wrote or quoted:
>> On Thu, 8 Apr 2004 16:11:50 +0000 (UTC), Tim Tyler
 wrote:
>> >r norman  wrote or quoted:
>> >> On Wed, 7 Apr 2004 16:38:52 +0000 (UTC), Tim Tyler
 wrote:
>> >> >r norman  wrote or quoted:
>
>> >> >> The statement really applies to hair colors. 
Many organisms can
>> >> >> produce structural colors including green and
blue in cutaneous cells.
>> >> >> The picture shows skin color, not hair color.
>> >> >
>
>> >> >Perhaps try these links, then:
>> >> >
>> >> >Blue:
>> >> > * Mandrill:
>> >> >   http://www.geometer.org/beginner/mandrill.jpg
>> >> >   http://www.mindysmem.org/gfx/mandril1.jpg
>> >> >   http://www.kevinschafer.com/es/images/eslgv7.jpg
>> >> >
>> >> > * Blue monkey:
>> >> >  
http://spinner.scis.nova.edu/Faculty/sumitra/safari2001/baboon/bluemonkey.jpg
>> >
>> >[...]
>> >
>> >> Sorry, I don't see a clear real blue pigment (or
interference color)
>> >> in the fur.  Some pictures might possibly have white
hairs that show a
>> >> bluish tinge.  Only one shows real blue and, not knowing
enough about
>> >> mandrills, might still be skin coloration.  Is there a
citation to a
>> >> chemical pigment that is blue or to a specific
semi-crystalline array
>> >> of reflective molecules that produce a structure blue
color in hair?
>> >
>> >The most-clearly-blue image so far.
>> >
>> >A mandril mane:
>> >
>> >  http://www.das-tierlexikon.de/mandrill_bild.htm
>> >
>> >*Surely* this one can leave no possible shadow of a doubt that the hair
>> >really does contain a blue pigment.
>> 
>> The shadow of doubt is an enormous black hole.  The nose clearly has
>> bright blue skin color, but the fur is not at all blue.
>
>Did you *actually* visit the site?
>
>My paint program reports the hair of the mandril's mane as:
>
>  R:56 G:69 B:103
>
>Pretty damn blue - IMHO.
>
>> Check any web site dealing with mandrills. None that I could find that
>> described color patterns in some detail and depth even hinted at blue
>> or even bluish color in the fur. Gray and olive-brown OK, blue NO.
>> 
>> And then you might want to look at the scientific literature:
>>   P. Sumner and J.D. Mollon
>>   Colors of Primate Pelage and Skin: Objective Assessment
>>      of Conspicuousness
>>   American Journal of Primatology 59:67-91 (2003)
>> http://vision.psychol.cam.ac.uk/jdmollon/papers/sumner_mollon2003.pdf
>> 
>> Their Figure 4 clearly shows a variety of fur colors (chromaticities,
>> actually) with absolutely none in the blue range.
>
>If table 1 is anything to go by, one data point represents a mandrill.
>
>Perhaps they failed to sample from a blue area.  Consequently, figure
>4 says little or nothing about the colour of some mandrills mane or
>rump hair.
>
>> Skin color was distinctly different. Yes, mandrills were included in 
>> their sample of 31 species of primates. The caption to Fig. 4 states: 
>> "The primate fur has a restricted range of chromaticities that lie in a
>> white-yellow/orange color direction. Lying on roughly the same
>> chromaticity axis, close on the opposite side of white, is the blue
>> skin displayed by some catarrhines."
>> 
>> Here is the opening of their discussion section:
>> 
>> "Gamut of Chromaticities Presented by Primate Pelage"
>> 
>> "The range of fur chromaticities displayed by primates is restricted
>> because mammalian coloration is determined chiefly by melanin
>> pigments. Different  combinations of pheomelanin and eumelanin (or
>> their absence) can supply a small range of colors from reddish-brown
>> or orangish-yellow to white, gray, or black. In nature, orange
>> coloration is often produced by carotenoids [Nassau, 1983], but these
>> pigments do not appear to be used in mammalian fur. It has been
>> reported that there are no detectable concentrations of carotenoids
>> even in the very orange fur of lion tamarins and orangutans [Slifka et
>> al., 1999]. In addition, the good agreement between the measurements
>> of pelts and live animals indicates that pelage chromaticities do not
>> change much with the environment or the diet of captive animals.
>> However, it is undeniable that direct sunlight does cause some
>> bleaching of fur color, which moves the fur?s chromaticity toward
>> white, and raises its luminance."
>> 
>> "As Fig. 5 shows, chromaticities of catarrhine skin can deviate from
>> this restricted distribution of fur. The blue coloration displayed by
>> species such as Mandrillus sphinx and Cercopithecus aethiops is caused
>> by Rayleigh scattering [Nassau, 1983], whereby small particles scatter
>> short-wavelength (blue) light more strongly than longer-wavelength
>> (red) light. "
>> 
>> In other words: no blue pigment.  Structural blue in skin only, not in
>> hair.
>
>It also apparently claims that the blue colour is an artefact of
>small particles scattering blue light - while red and green light
>is absorbed.
>
>``As Fig. 5 shows, chromaticities of catarrhine skin can deviate from this
>  restricted distribution of fur. The blue coloration displayed by species 
>  such as Mandrillus sphinx and Cercopithecus aethiops is caused by 
>  Rayleigh scattering [Nassau, 1983], whereby small particles scatter 
>  short-wavelength (blue) light more strongly than longer-wavelength (red) 
>  light. The blue caused by Rayleigh scattering is often called ??Tyndall 
>  blue?? (blue sky is an example). Thus the range of blues in
>  the mandrill and vervet have very similar chromaticities to the blues of 
>  the sky. In these primates, the incident light of shorter wavelengths is 
>  scattered toward the observer by small particles in the skin, whereas 
>  the longer wavelengths pass through and are absorbed by an underlying 
>  dark layer of melanin. The larger the scattering particles, the less 
>  saturated the blue color will be, because more middle
>  wavelengths will also be scattered.''
>
>They distinguish (12 lines down from the quoted section above) between 
>blue casued by scattering, and blue caused by pigmentation.
>
>My understanding is that the *definition* of pigment is that it is a 
>substance that produces a colour when illuminated.
>
>AFAIK, it doesn't matter whether the colour is produced by reflecting 
>light, absorbing and partially re-radiating it, or transmitting some 
>components and scattering other ones - *all* that matters is that a 
>colour is produced.
>
>Consequently, I don't know about their notion that the mandrill's nose 
>contains no blue pigment either - but I *do* know is that both the nose
>and the mane of the mandrill in the photo are plainly blue - as any child
>would be able to see.

This is really getting a bit out of hand.  I don't have a Mandrill
handy -- probably the Detroit Zoo has one, but it is a long drive.  I
don't trust colors in photographs unless they have been done
photogrammetrically.  That is why I deny that the mandrill has a blue
"mane". That and what I know about animal colors.

I have been interested in animal pigments for some time -- I used to
have students do experiments on frog and shrimp chromatophore -- so I
am familiar with the chemistry and physics of animal colors and I do
know how to research the scientific literature. None of my
investigations have produced even a hint of mention of blue colored
hair/fur/pelage in either a Mandrill or in any mammal.  I have never
doubted that the skin has a very distinctive blue color. The piece you
quote from my citation very specifically differentiates the color
range in skin from that in hair.  You suggest that the authors may
simply have failed to sample the rump or mane hair.  I can't say one
way or another, but a research effort done specifically to investigate
the full range of colors found in primates and which contains a
section titled ""Gamut of Chromaticities Presented by Primate Pelage"
is very unlikely to ignore an obvious thing like that.  Furthermore,
the authors very specifically point out the fact that none of their
hair samples produced a blue color when measured photometrically
whereas the skin distinctly did. They are certainly not going to have
missed such an "obvious" case had the fur been actually blue. From my
very first post in this thread, I commented specifically about hair
color, often remarking that many animals (including mammals) can
produce a wide variety of skin colors.  The whole gist of the thread
is the overall color pattern of mammals which is determined by fur
color, not specific color marking determined by patches of bare
exposed skin.

The difference between "pigment" color and "structural"
color is quite
standard in discussions of the cellular basis of animal colors.  In
that context, the word "pigment" always refers to a chemical with a
specific absorption spectrum that produces the apparent color in
distinction to "structure" which refers to molecules which do not
produce color unless they are arranged in a particular physical
configuration that produces either Rayleigh scattering or interference
patterns or some other optical trick that results in color. That is,
"pigment" in this instance is a technical term used in a specific
technical sense.

Please don't post any more url's to photographs.  It is virtually
impossible to capture true color in these.  If you want to continue
the argument, please produce an authoritative citation stating that
some mammal has truly blue colored hair, not the faint bluish tinge
that is sometimes apparent in gray or white hairs.
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