Explanation:

The Red Data Book, information for endangered mammals and birds are more extensive than for other groups of animals and plants, coverage is also given to less prominent organisms facing extinction.
The pink pages in this publication include the critically endangered species. With passing time, the number of pink pages continues to increase which indicates increasing number of critically endangered species.
Green pages are used for those species that were formerly endangered but have now recovered to a point where they are no longer threatened. So, increase in green pages indicates the increase in conservation efforts.
Do you know?
A taxon is Extinct in the Wild when it is known only to survive in cultivation, in captivity or as a naturalized population (or populations) well outside the past range. A taxon is presumed Extinct in the wild when exhaustive surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout its historic range have failed to record an individual.
THINK!
Critically Endangered(CR)
Endangered(EN)
Vulnerable(VU)