Late 19th century. From post-classical Latin achromos or its etymon ancient Greek ἄχρωμος colourless + -ous. Compare earlier achromatous, and also achromatistous and achroous.
He worked to be a writer. Sadly, Joe’s prose was achromous and dull. Routinely sprinkling in words which were overused on social media did make him seem trendy so his books sold well.