Since Colbert died prematurely it's not surprising that the "memoirs" are not actually written by Colbert. The practice of compiling memoirs was quite common, though.
There's also a biography in English of Colbert:
Title: Auguste de Colbert: aristocratic survival in an era of upheaval, 1793-1809 /
Author(s): Ojala, Jeanne A.
Publication: Salt Lake City : University of Utah Press,
Description: xii, 199 p. : ill. ; 24 cm.
Standard No: ISBN: 087480124X; LCCN: 79-4872
Descriptor: Soldiers -- France -- Biography.
Militaires -- France -- Biographies.
Named Person: Colbert, Auguste François Marie, baron de, 1777-1809.
Colbert, Auguste François Marie, baron de, 1777-1809.
Named Corp: France. Armée -- Biography.
France. Armée -- Biographies.
Note(s): Includes index./ Bibliography: p. -194.