This definitive of Hong Kong (Scott 185-98) had scores of printings. Some values were reprinted 15 or 18 different times. It's possible to accumulate many examples from each denomination and see all different shades.
Gibbons only lists stamps that have a very obvious difference in shade, though Gibbons does list the printings in the Elizabethan catalogues issued c. late 1970s to 1985. Not sure if this relates to the question you are asking, but sharing a little info.