Color and shades are one of the most overdone areas of our hobby. During the earliest years of collecting, before 1900, there were simply not enough new stamp issues for the amount of time that collectors had to devote to our hobby. Collectors then parsed and refined their specialties and one way to do this was by shade. Collecting this way ignores the reality that certain colors, blues and reds especially, degrade and change over time especially depending on exposure to light or air. What we call different shades today are often due merely to different handling criteria on 100 year old stamps that may have well been printed next to each other on a sheet. When significant shade variations exist, they should be saved and studied. When different printings at different times produces different shades then of course they should be saved. But just two anecdotes to end this post. Many years ago I did a year long study on the three major shade differences of the United States 3c 1851-the ordinary red #65, the rose pink #64b, and the true pink #64 (the last two were PFC certified copies (though defective). I put them out on a corner of a table in our office where every day they received full office fluorescent light. At the end of a year neither of the two pink shades would have retained any chance of being certified as the valuable shades. And the second story is about one prominent expertiser who has a predilection for Pigeon Blood pinks (Scott #64a) the super rare 3c 1861 shade and who will give certificates on this rare stamp when the shade exists mainly in his own eye. Paying big money for minor shade varieties is dangerous.
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