That instrument represents the last of the Venanzio Morino-era Morinos (i.e. when the man himself was still at Hohner, but not necessarily having a direct hand in making them). The earlier generation Morino M had a single stripe down the middle of the grille and it had the rectangular bass layout. They came in colours (white, red, grey) and could have the pearly keys or off-white, slightly striped keys. There was also an alternative older grille design (example of a red one with the different grille on ebay: https://www.ebay.com/itm/Akkordeon-...rn-gestimmt-und-uberholt-Casotto/124280589814).
The later generation Morino M's (Giovanni Gola-era) have three stripes down the grille, trapezoidal bass and, as far as I've seen, were always black.