Synonyms that are in the dictionary are marked in green. Synonyms that are not in the dictionary are marked in red.
Antonyms that are in the dictionary are marked in green. Antonyms that are not in the dictionary are marked in red.
This shows users a few options, including 'Time left in chapter' option is grayed-out and says ',' it means that book cannot show normal page numbers.
Source: https://screenrant.com/amazon-kindle-books-see-page-numbers-how/