At the age of fifteen Colby completed his education in the common schools of his native town and went to Exeter, New Hampshire, to learn the printing trade.
Colby's first work in printing was done on an edition of Scott’s Family Bible. In 1836 he moved to Boston and began his twenty years’ connection with the Boston Daily Post, during which time he advanced from journeyman printer to night editor. Through a fellow printer, William Berry, with whom he became familiar while in the service of the Post, he was introduced to Charles Crowell, Mrs. J. H. Conant, and other spiritualist mediums. As a result of noting the reports of manifestations of the spirit world and of attending seances where he received what appeared to him indubitable testimony to the truthfulness of spiritualism, Colby joined with Berry and in 1857, “in obedience to a company on high, unfurled the Banner of Light, " a weekly spiritualist paper, “devoted to the advocacy of the Spiritual Philosophy and Phenomena. ”
The avowed purpose of the paper was the publication of spirit messages through the mediumship of Charles Crowell. Colby firmly believed that truth could best be served by a careful publication of all alleged communications from the “sphere of light” to the “mortal state, ” together with the supposed evidence for them, and that thereby man could come to know himself truly as a spiritual being in his eternal relations, instead of confining himself to sense knowledge of his temporary material bonds. He had a fervent conviction that the revelation of spiritual truth by the Banner of Light would revolutionize the world. Berry was killed in the Civil War; Colby continued to serve as editor of the Banner of Light until his death.
The whole life of “Luther the veteran, ” was centered in this paper and in his defense of the unpopular cause of spiritualism. Though not personally a prominent man or a writer of books, his influence as editor of the Banner of Light was widespread. The paper was his pride both as to its high moral tone and as to its attempt to serve nothing but the truth. Its typographical form received his close attention, and the paper was a model of neatness and accuracy.
Throughout his editorship he followed the liberal policy enunciated in his first statement, that we “shall not believe everything but shall not refuse to listen to what is said. ”
Colby was genial, honest, upright to the core, and, though excitable and impetuous, extremely generous. He was of large stature, robust physique, and temperate habits. He possessed a mind comparatively free from conventional dogmatism and narrowness, and was given neither to theological speculation nor to church practises.