Most dentists receive or purchase their shade guides in dental school and continue to use them throughout their careers. How old is your shade guide? In today's day and age of infection control it has become necessary to disinfect and or sterilize our shade guides after each use. There are glazes and stains, which are applied to all shade guides. These will be removed over time with repeated wiping or soaking in liquid disinfectant/sterilant liquids. When this occurs the visual appearance of the tabs will change. The result? Your A-2 tab does not match your lab's A-2 tab.
Autoclaving your shade tabs will not cause these stains and glazes to be removed over time. All currently sold shade guides by both VITA and Ivoclar-Vivadent are now fully autoclavable.
If you have shade guides that are several years old, and you have been wiping or soaking them with liquid disinfectant/sterilant liquids, it would be wise to consider purchasing new shade guides.
Even one remake due to shade because of an older shade guide would cost you (in chair time) more than the cost of replacing several shade guides. If you have questions about whether your guide can be autoclaved because it is a few years old, I would recommend contacting the manufacturer.