Shades and their nomenclature are arbitrary. And people’s perception of color is as well. The average person can see about one million different shades. Some people with a genetic mutation can see up to one hundred million. My gut feeling is that Scott uses about 2500 different shades as names in their catalog, though such generic terms as “dull red” often mean quite different things on one stamp than it means on another stamp. But often times shade variations just seem arbitrary to me. Scanned above are two rare shades of the 3c 1861 Dull red. They are the Pink (Scott #64) on the left and the Pigeon Blood Pink (Scott #64a) on the right. Each has just been given a very recent certificate of genuineness from William Weiss who is a very well thought of and recognized expert. The difference in shade is very small and frankly not at all obvious to me. And yet the Pink (left) catalogs $900 and the Pigeon Blood Pink (on right) catalogs $5000. This is probably why many collectors don’t involve themselves too much with shades.