See Muscari muscarimi Medik., synonym Muscari moschatum Willd., for more information on the species.  The Musk hyacinth, Muscari muscarimi Medik., is a very distinctive plant, and I have found no reference to the dark blue colour form listed here, although the other colour forms are possible as the species is somewhat variable, and almost white flowers and forms with a distinct pale blue tinge to the flowers are known.  The three Muscari moschatum colour forms listed in the catalogues could also be Muscari botryoides as flowers in shades of blue, pink and white have been known since at least the early 19th century and probably much longer.