I got my chart from the Marans Chicken Club USA. I have seen other charts on-line, but this is the only chart I have a hard copy of and generally what I use to evaluate eggs.
There was a High School Class in Avery, North Carolina studying the genetics of rare breeds of chickens. The Cream Legbar Club donated hatching eggs to the class to hatch and they send back information on the class project. One of the sample assignments that they sent was the classification of egg colors. They received Cream Legbar, Auracana, and Ameraucana hatching eggs and used the Auracana color chart to classify them. Even with every student in the class using the same color chart I am guessing that there was a variation of numbers listed. I would have loved to grade that class assignment to see the deviation in answers.
The class received Marans, Penedencesa and other dark brown eggs. I noticed that the class used two different Marans charts for that portion of the assignment and likewise would have liked to grade that assignment to see how one card compared to the other and how the subjectivity from one student to the next effected the range of colors listed.
It think the article on the class project is in the 3rd Quarter 2013 Newsletter of the Cream Legbar Club.
Note: The same color card will show up different depending on the lighting it is photographed in. I would assume that my color and yours would be about the same if put next to each other in real life. My photo above was taken with flash. The flash I have noticed make things look lighter than when I turn the flash off.
Cameras and online colors seldom look like the natural object in reality - one reason that I don't post pics of my egg colors. My camera makes the eggs look deeper and more colorful than in reality.