Old printer's good German book in sickly green (9)
I believe the answer is:
gutenberg
'old printer's' is the definition.
(Gutenberg introduced the printing press to Europe)
'good german book in sickly green' is the wordplay.
'good german' becomes 'gut' (I've seen this before).
'book' becomes 'b' (abbreviation for book).
'in' is an insertion indicator.
'sickly' indicates anagramming the letters (I've seen this in other clues).
'green' anagrammed gives 'energ'.
'b' put inside 'energ' is 'enberg'.
'gut'+'enberg'='GUTENBERG'
(Other definitions for gutenberg that I've seen before include "German printing pioneer" , "German printer of a 15th century Bible" , "He invented movable-type printing" , "Publisher" , "Pioneer printer" .)