The general appearance of Newton's parakeet was similar to the extant "Psittacula" species, including the black collar, but the bluish grey colouration set it apart from other members of its genus, which are mostly green. It differed from its Mascarene relatives in some skeletal details, including in that the internal margin of the mandibular symphysis (where the two halves of the lower jaw connected) was oval instead of square-shaped when seen from above, and in that the upper end of the humerus (upper arm bone) was less expanded than in the Mascarene grey parakeet and the echo parakeet.