Identifying Stamp Colors

This article explores how collectors perceive stamp colors and many of the common color misconceptions. It is truly unfortunate that so many catalog and other references use color as a way to identify stamps since it is by far the least reliable and most subjective identification method. The scope of this article is limited to a collector holding a stamp in their hand and looking at it. Trying to accommodate the use of technology (scanned images, saving images, viewing images) is far beyond the scope if this article since it adds many additional layers of complexity.

We need to have the correct perspective about colors and where they are generated. Stamps do not possess color but rather stamps reflect wavelengths of light which are perceived by our brains. “We know from psychophysical and neurophysiological investigations that color is created somewhere in the brain, although the exact location of this process is still unknown, and we even have no idea what entities the sensations called color are . . . In short, colors appear only at a first naïve glance to be located in objects.” (Backhaus & Menzel 1992, p. 28) Colors are perceptions and these perceptions differ from one person to another. We can say that color is a ‘psychological property of our visual experiences’ when we look at a stamp, not a physical property of the stamp.

So the first color challenge is that we all have different eyes and brains. The second challenge in understanding how a stamp’s color is impacted by viewing it in different lighting conditions.

Let’s begin by understanding how as stamp collectors we perceive colors. We see colors when a stamp absorbs some of the wavelengths but reflects others. The reflected wavelengths enter our retinas which in turn fire neural connections to the visual cortex. The visual cortex is the part of the brain that converts the signals into a perceived color. Our retinas have two types of cells; cones and rods. The rods are photoreceptor cells which are most activated when in low or dim lighting; most humans have around 120 million rods in a retina. The cones contain color-detecting photo pigment cells, most humans have three types; red, green, and blue (this is called ‘trichromacy’). Each of these approximately 6 million cone cells is sensitive to different wavelengths of light that is being reflected into our eye.

But since the color of a stamp come from reflected light wavelengths this sets up a strange fact. When you look at a red stamp, you are seeing the red parts of the lighting spectrum that is not on the stamp but rather is being reflected off the stamp. The actual color of the stamp is anything but red. However it would be strange to walk around saying “that stamp is anything but red” so we just say “it is red”.

Another interesting fact is that women typically are much better at detecting colors than men because they have more cones in their retinas. It is estimated that 12% of all women actually have a fourth, additional color-detecting photo pigment cell (having four types of cones is called tetrachromacy). People who have this trait can detect as many as 100 million additional colors. And on the other side of the scale, men are more likely to have color vision deficiencies (there are 9-12 different types of color deficiencies). As many as 10% of the male population may have at least one type of color vision deficiency. There are also notable color vision deficiency deltas between geographic and demographic populations. So the take away here is that men are much less likely to correctly identify color than women and that variations between how any two humans perceive a color is almost inevitable.

But how we perceive color is more than rods and cones. As previously stated, the visual signals are sent to our visual cortex. Our past visual experiences with things influence our perceptions of color. This is called ‘color constancy’. Experiments have proven that our perceived colors can be influenced by color constancy. In other words if you look at a banana, you expect it to be yellow and impacts how your brain processes the color you think you are seeing.

Your past visual experiences with objects also influence your perception of color. This phenomenon is known as color constancy. Color constancy is a type of bias that our brains introduce which influence how we are perceiving a color of an object. For example, if you looked at a banana under a red light (making it look orange), you likely would still perceive the banana to be yellow. This influence opens the door to potential mis-identification of a stamp; if you know that a certain color is quite rare, say ‘pigeon blood pink’, your brain may sway your judgement when you look at a stamp.

The ambient light in which we view a stamp has an incredible impact on the color we perceive it to be; even something as simple a ‘daylight’ has a significant amount of variance. For example, the chromatic axis runs from a pinkish-red in the morning, more of a blue-white in the afternoon, and over to red color near sunset. We learned that the colors we see are actually reflected wavelengths so it only stand to reason that the wavelengths of the ambient light will affect our perception. If we view a stamp under a typical yellowish incandescent light bulb it will emphasize the warmer colors because there is additional red and green wavelengths in the light itself to reflect off the stamp and into your eye. But if we view the same stamp under a typical fluorescent light, the ‘cooler’ blue color wavelengths are emphasized. So if you want to be a serious about identifying stamp colors you need to define and be highly consistent with your ambient lighting conditions.

There is also a phenomenon called ‘metamerism’ which occurs when two stamps which are not the same the color but appear to be the same under certain lighting conditions. The image below shows two identical gray samples but how they can appear different colors under certain lighting wavelengths (metamerism). The hues that are most likely to have metameric problems include browns, tans, lilac, gray/blues, and gray stamps.

Additionally, be aware that background colors can influence how you perceive the color of a stamp. The gray bar in the image below is the exact same color across its entire face yet because of the background our brain drives us to see it as being a gradient. When we remove the background and replace it with a solid color, the gray bar now appears to be the same color. This highlights the need to have a consistent background when trying to identify stamp colors.

Lastly, it is important to keep in mind that printing inks and paper colors are ephemeral over time; stamp colors are the definition of a ‘moving target’. Color standards companies like Pantone and Munsell replacing their color guide references every 2-3 years. After hundreds of years of development mankind has not been able to invent inks, paint, or even pure pigments that retain their original color over time. Purchased color guides can only be considered to be accurate for a few years after they are printed. But moreover it is important to remember that the provenance of old stamps is never known. Light exposure, exposure to atmospheric pollutants, generations of soaking, checking for watermarks, etc. all have an impact on the color of a stamp over time.

There are a number of thing a hobbyists can do to develop a good ‘color eye’. Below are a few recommendations based upon my experience as a color matcher.

• 1. Define your ambient light sources and never try to judge a stamp color in different lighting conditions.
  
  
• 2. To prevent other colors in your field of view from influencing your judgement, use a white card with a cutout in the middle to place over the stamp.
  
  
• 3. Never try to judge a stamp color in direct sunlight, the bright sunlight introduces ‘shine’ to the surface of the stamp.
  
  
• 4. View a stamp color for no more than 5 – 10 seconds at a time. if you stare at it longer than this, your brain begins to compensate for any perceived differences.
  
  
• 5. Define (and adhere) to a distance that you hold the stamp at, the stamp surface should be held at approximately a 30-degree angle to light source.
  
  
• 6. Build a large reference library of the same stamp and refer to it often to keep your color eye tuned.