A must read about colors

Good morning Robins, Attached is a post about colors and pigments and how we
see them. It has been a topic on the Daylily Robin I belong too and this was
an excellent posting.

I obtained permission from the author to post it on the Iris Robin. It is
rather long but worth the read.

Bob Benbow Camdenton Missouri Zone 5 

 Subject: [DAYLILY] The science and legerdemain of whiteness

Hi Robins --

Pete Wetzel, Central MD, region 3, boundary of zones 6 & 7

A new seedling bloomed for me a few days ago which shocked
my senses.  As I strolled my seedlings and first noticed it
that morning, the sun was just peeking above the trees.  It
appeared to be the least yellow of any daylily I had ever
seen ... by far! (the word "breakthrough" immediately sprang
to mind).  The color impression was of a voluptuous green
throat surrounded by purest white ("whiter than white").
That was the case whether looking face-on, from the side, or
at the backside of the flower.

Because my personal prime directive in hybridizing is
to "get the yellow/melon out" of daylilies, I took notice.

What is remarkable is that this flower was not a pure near-
white at all, but the palest of lavenders.  It has multiple
generations of my near-white breeding in its background, so
the underlying color has been purged of as much yellow/melon
as I am able to muster.  That surely helped.  But the faint
lavender wash is what made the ultimate difference.

The science of whiteness is a seriously important commercial
enterprise.  Whiteness sells -- white teeth, white paper,
white fabrics.  So there have been countless commercial
studies of what appeals to the human eye.

The normal human retina contains three kinds of color
receptors (cones).  [There is a rare mutation among some
women, which gives them a fourth type of cone.  I haven't
been able to find specific information about the color
sensitivity of this extra cone receptor.]  But the three
common receptors that most of us have are all sensitive to
quite a broad range of light.  Far from being optimally
tuned to the standard primary colors, "red-green-blue", the
three colors at which your cones have peak sensitivity
are "blue-violet, green-yellow, and yellow-green".  The
latter two cones obviously have a pretty close spectral
sensitivity to one another.  That is because they only
recently (on the evolutionary time scale) diverged from one
another.  The newest evolutionary advance, the yellow-green
cone, *is* significantly more sensitive to red light.  So
our brains work their legerdemain, and allow us to
adequately perceive red.  This ability is only shared by
humans and the highest old-world primates.  It is said to
have evolved in order to better distinguish/identify
ripening fruit.

How does the color sensitivity of our three types of cones
influence our perception of whiteness?  As a seasoned
research scientist, I'm taking the evidence and launching
into my own hypothesis here.  We have two types of cones
which are highly yellow-sensitive, and one which is blue-
violet sensitive.

Objective whiteness, as defined by scientific instrumental
sensors, represents perfect 100% reflection in all
wavelengths of light (all colors).

But subjective whiteness, as perceived by our three
imperfect cone receptors, will saturate the two yellow-
sensitive receptors and only one blue-violet sensitive
receptor.  Thus it will appear to us to be more yellow than
it actually is.

So to compensate, human perception/judgement has correctly
given more weight to its blue-violet cones when evaluating
subjective whiteness.

It is an established fact, based on countless studies, that
humans (in most cultures) will identify an object to be
whitest if it reflects nearly 100% of blue/violet light but
reflects notably less than 100% of yellow-green and green-
yellow light.  In other words, we have a sensor bias that
leads us to identify faintly blue-violet hues as being more
white than yellowish hues, ***even though*** the objective
non-human sensors show that the more yellowish hues actually
reflect more total light, and are therefore more
(objectively) white.

There is another, purely environmental argument which might
cause us to prefer objects that are more blue compared to
objects that are more yellow.

Consider the natural objects, with which we evolved, that
appear white.  The most abundant of them (to us) are clouds,
snow, quartz rocks, the teeth in a human smile or a
predator's snarl, and fresh plant fibers (flowers, tubers,
fruits [think apple], fresh-cut wood fibers [think paper],
and raw materials for fabric [e.g. cotton]).

The sky is blue.  So clouds are viewed through a not-quite
transparent "haze" of blue-tinted light.  Air molecules
selectively scatter blue light more than red/yellow.  (Trust
me, I'm a research meteorologist <g>).

Clouds are among the only things in our environment that
steadfastly hold their (blue/)white color.  Snow cover
accumulates dust and dirt which tend to reduce its whiteness
with time.  Dust and dirt tend to be yellowish or brownish
(predominantly iron oxides and organics).  Brilliant white
pure quartz is also subject to being color-tainted by iron
oxides, which turn it reddish/yellowish/brown.  There aren't
any compensating "bluing" agents.  Teeth turn more yellow as
they get stained by the various organic compounds that we
eat.  Plant fibers (apples, potatoes, paper, wood, cotton,
senescing white flowers) all consistently turn more
yellow/brown as they age.

The cumulative result of this environmental influence:  I
speculate that we attribute added "whiteness value" to those
rare, special things that resist acquiring "yellowness" with
the passage of time, most notably clouds, which have a blue
cast because of the sky through which we view them.

So this enviromnental "bias toward things that reflect blue"
is added to the physical bias that is built into our cone
receptors, as discussed above.

Now back to daylilies.  Rare (or even non-existent) is the
daylily which does not possess some yellow coloration in
some part of its bloom.  I ask you to try to gather an
overall impression of your daylily beds viewed from a
distance, and judge for yourself -- What color dominates?
For me, without exception, in all the gardens I've seen in
person or via a photograph, there is a dominant yellowness.

In the human quest for "whiteness", we seek to purge the
yellowness.  In fact we would hope to even exchange it for
a "blue-violetness" which dims the overall reflectivity of
the flower, but which is more pleasing to our eye.

The commercial interests, who seek to gain your favor by
selling you things which you perceive as white, have long
recognized this bias.

There are four important ways that are used to make
things look more white:

The first is bleaching.  Bleaching fabrics, paper or teeth
happens to increase the reflectivity in the blue range more
than it increases the reflectivity in the yellow range.
This is the simplest first line of defense against
yellowness.

The second is adding a blue colorant.  Doing so actually
*reduces* the overall reflectivity, particularly in the
yellow range.  But because of the human eye's bias, many,
many objective preference studies have shown that humans
will prefer objects which have been died subtly more blue
as having more "whiteness" -- even though their reflectivity
has been reduced.  Some laundry detergents contain blue dye
crystals.  The "blue-hair" ladies in your local daylily
clubs have found this approach to work to their advantage.

The third is perhaps the most "honest" way to increase
whiteness -- to inject pigments that actually reflect more
light.  The most successful of these is Titanium Dioxide.
My 81 year old father is a Chemical Engineer who worked in
the pigments department at DuPont, Co. (researching newer
and better paint colors).   In the 1950's and early 60's he
helped pioneer the use of TiO2 as a colorant.  Titanium
Dioxide has a greater reflectivity in visible and
ultraviolet light then any other practical pigment.  It
continues to be widely used in many, many products ranging
from energy efficient urban roofing to toothpaste.

But Titanium Dioxide strongly absorbs ultraviolet light.  UV
light is invisible to the eye, so your first response to
this should be "so what?"  But this is a critical fact when
considering the fourth and most sophisticated method of
increasing an object's perceived whiteness.  That is the
addition of fluorescent agents called "Optical
Brighteners".  These "dyes" actually absorb ultraviolet
light and convert it to visible blue light.  The amazing
properties of these dyes is that they "reflect" more blue
light than they receive.  They essentially "glow in the
dark" -- they effectively have something like a 120%
reflectivity in the blue end of the visible light spectrum.

In order to make your product the whitest it can be, you
first bleach it, then you may want to add a blue colorant,
and finally you add an optical brightener.  In many
applications, you don't want to also add TiO2 because it
conflicts with the optical brightener by absorbing the
ultraviolet light rather than making it available to the
flourescent optical brightener to be converted to visible
blue light.

But back to daylilies once again.  You can't bleach them.
Until genetic engineering gets a lot more sophisticated, you
can't add titanium dioxide and you can't add optical
brighteners.  But you can tint your whitest daylily with a
blue-lavender wash.  From my comparisons of this first year
seedling with GENTLE SHEPHERD (which continues to be the
whitest daylily on the planet), this seems to work.  It
reflects a tiny bit less light;  but it is more pleasing.
To me, it looks whiter, both when viewing it in person
(direct sunlight or shade) and when viewing the digital
photos taken under these different lighting conditions.

But I'm not getting too excited yet about any breakthrough.
This first year seedling has rather ratty foliage -- lots of
leaf streak.  I has a bud count of 6, which I judge by
comparison with other first year seedlings here as ordinary
at best.  There's just a "hint and a promise" of future
glory here.

Hope those of you who are conventionizing are enjoying your
cool, clear Sunday.  Sorry for the looooooooooooong post!

-- Pete

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