Scott 2940 - 55c Alice Hamilton, MD - Color Variety?

The 55c Alice Hamilton, MD stamp (Scott 2940) is listed in the Scott catalog with no color varieties listed, yet the on-cover examples below suggest that there is a lighter and darker green variety:



The top example (damaged stamp) seems to be the color that most of my off-cover stamps display; whereas the bottom example seems to show a darker color green.

Has anyone ever noticed this before or is it just not significant enough of a variety to be catalog listed?

The cross hatching throughout, as well as the "U" of USA show that the bottom stamp is very heavily inked. Even if this one were the same ink color, it would appear darker. I always 'hit' my color varieties with long and short range UV light. If there are different components in the ink, they would perhaps show up this way. Using UV light, you can see nuances of color better in a dark room, and after your eyes have adjusted to the low lighting.

It wasn't until just a few years ago that Scott recognized the lighter colored versions of both Margaret Mitchell (2168b) and Hugo Black (2172b). Perhaps something similar will happen with this issue. Only time will tell.
Added: After taking a look at my 2940 plate blocks, I noticed that the color on B1 is noticably lighter than the colors on B2 & B3. But a quick look at similar blocks on ebay leads me to believe that the color variation is probably independent of the plate number.

Wt1, Several years back a stamp dealer / collector in Cleveland, Ohio by the name of Steven Esrati issued a newsletter called "the Plate Number".
It was basically meant as a round robin for a study group that specialized in the Transportation Coils, but later on the Great Americans series was also included. An awful lot of info on these Great Americans was eventually printed, including color ( and other ) varieties.
The whole set of newsletters is available at the PNC3 website, www.PNC3.org

Peter