SERIES 02. THE SCIENCE OF COLOR
We often describe skin in familiar terms.
“It looks bright.”
“There is some redness.”
“It looks more yellow.”
These descriptions seem simple until we try to explain how bright, how red, or how different one person’s skin color is from another’s.
The same skin can appear slightly different depending on light and surrounding colors, and different observers may describe what they see differently.
To study skin color, we therefore need a shared language that allows visual differences to be recorded and compared.
One such language is the CIE L*a*b* color space.
Reading skin color through three coordinates
CIE L*a*b* represents color along three dimensions.
L* represents lightness.
a* represents the direction between green and red.
b* represents the direction between blue and yellow.
Within the complete CIELAB color space, both a* and b* can have positive or negative values.
Positive a* moves toward red, while negative a* moves toward green.
Positive b* moves toward yellow, while negative b* moves toward blue.
Human skin, however, occupies a much narrower region of this color space.
Within the human skin range used in COCORY’s skin-color analysis, measurements fall within the positive a* red direction and positive b* yellow direction.
This means that when we analyze human skin, the key question is not whether a* or b* is positive or negative.
Instead, we examine how much redness and yellowness are present and how those two components relate to each other.
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L*: How light is the skin?
L* represents lightness.
Values move from darker toward lighter as they increase from 0 toward 100.
This gives us a more specific way to compare what we casually describe as lighter or darker skin.
But similar L* values do not mean that two skin colors are the same.
Two people may have almost identical lightness while one has a stronger red component and the other a stronger yellow component.
Lightness is only one dimension of skin color.
a*: Reading redness
a* represents the direction between green and red.
For human skin measurements, we primarily work within the positive a* region—the red side of this axis.
In skin analysis, a* is therefore useful not simply for asking whether skin is red or green, but for comparing the relative degree of redness present in the skin.
Two skins with similar lightness can appear different when their a* values differ.
Yet a* alone cannot describe the complete color of skin.
Human skin also contains a yellow component represented by b*.
b*: Reading yellowness
b* represents the direction between blue and yellow.
Human skin also generally occupies the positive b* region, allowing us to compare its yellow component.
But this leads to an important distinction.
A higher b* value does not automatically mean that a person has warm skin.
Human skin contains red and yellow components at the same time.
Two people may both have relatively high b* values, but if their a* values are different, the relationship between yellow and red within their skin will also be different.
So if we want to examine warm and cool tendencies more precisely, what should we compare?
b*−a*: Reading the relationship between yellow and red
One of the key values used in COCORY’s skin-color analysis is b* − a*
In human skin, both a* and b* occupy positive regions.
Understanding warm and cool tendencies therefore requires more than simply asking whether yellow is present.
What matters is the relative difference between the yellow and red components.
A larger b*−a* value indicates that the yellow component is relatively stronger in relation to the red component.
As b*−a* becomes smaller, the difference between yellow and red decreases, or the relative contribution of redness becomes greater.
This means that
warm skin cannot simply be defined as “yellow skin,”
and cool skin cannot simply be defined as “red skin.”
The relationship between these components matters.
COCORY’s approach to interpreting skin color
COCORY has long incorporated instrumental skin-color measurement into personal color analysis rather than relying solely on visual impressions.
After introducing skin colorimetry into its personal color process in 2014, COCORY continued to collect and analyze human skin-color data.
Rather than looking only at L*, a*, and b* as separate measurements, COCORY developed a method of using b*−a* to interpret the relationship between yellowness and redness.
This relationship became one of the key quantitative references used to examine warm and cool tendencies within COCORY’s proprietary Tone Formula.
Published academic research has also measured L*, a*, b*, and b*−a* and applied the resulting data to a tone-calculation formula developed by the COCORY Color Research Institute.
For COCORY, interpreting warm and cool skin is therefore not simply a matter of looking at someone and deciding that their skin appears “yellow” or “pink.”
It is a process of examining the measurable relationship among the components that form skin color.
One value does not determine a personal color
Does that mean b*−a* alone can determine whether someone is warm or cool—and ultimately determine their personal color?
No.
b*−a* is an important quantitative reference in COCORY’s interpretation of skin color, but
the warm–cool tendency of skin and the warm–cool characteristics of colors that harmonize with a person are not exactly the same thing.
A face contains more than skin color.
The lips, eyes, hair, facial contrast, light and shadow, and the person’s overall visual characteristics all exist at the same time.
Personal color analysis must therefore also observe what happens when different colors are actually placed near the face and compared.
Skin-color data is not the final answer.
It is one important reference for understanding a person’s color characteristics more precisely.
The same skin can produce different measurements
Measuring skin does not guarantee exactly the same numerical result regardless of when, where, or how the measurement is taken.
Human skin is not a uniformly printed color sample.
Results may vary with the instrument, settings, measurement location, and measurement method.
For skin-color data to be meaningful, it is therefore important to record not only the number itself but also
where, under what conditions, and by what method the measurement was taken.
If measurements collected under different conditions are treated as equivalent, the numbers may exist while the basis for comparison becomes less reliable.
Skin colorimetry therefore requires consistent and repeatable measurement conditions.
Why turn perception into data?
The purpose of measuring color is not to reduce people to numbers.
L* records lightness.
a* records the red component.
b* records the yellow component.
And COCORY uses b*−a* to examine the relationship between the yellow and red components of skin.
Together, these measurements transform expressions such as
“a little brighter,”
“more red,”
“more yellow,”
or “relatively warmer”
into information that can be recorded, compared, and revisited.
Numbers are not the conclusion of an analysis.
They provide another reference for understanding more precisely what we observe with our eyes.
COCORY’s approach is not to replace human observation with data.
It is to connect observation and measurement in order to understand human color more precisely.
NEXT JOURNAL
2-3. Is Olive Really a Skin Color?
Human skin can be measured within a defined range of colorimetric values.
So what does Olive Skin or an Olive Undertone, terms widely used in global beauty culture, actually mean when we look at skin through measurable color data?
In the next journal, we examine whether skin that appears olive and skin color as measured data are describing the same thing.
Setting the Standard for Color, for People.
