"A black book."
Translation:Een zwart boek.
I think you're right about the "e" usually being dropped from adjectives at the end of the sentence. I think this is true except for when nouns are omitted because they have been previously mentioned and it's understood what you're talking about, and there is an implied noun at the end of the sentence. E.g. "Koop je een tas? Ja, ik koop de zwarte". Are you buying a bag? Yes, I'm buying the black (one). Also, an "s" is added to adjectives when they follow words like iets, niet, and weinig, e.g. "iets moois" (something beautiful).
I think the "e" is not added to adjectives that are in front of "het" nouns if words like een, geen, elk, ider (indefinite pronouns) are in front of the noun. In this case I think you would say: Een zwart boek; Het zwarte boek; Het boek is zwart. The "e" is still added after "het" because "het" is a definite article.
Hope this helps! :)