Four hydroxide ions are bound to an aluminium ion. Aluminium hydroxide is amphoteric as well, and this is the ion it becomes in excess sodium hydroxide solution.
The coordination number is 4 and the geometry is tetrahedral. The whole ion carries a charge of 1-, and the metal is named as aluminate.
The solution is colorless. Unlike zinc, aluminium does not dissolve in excess ammonia. Sodium hydroxide solution dissolves both precipitates, ammonia dissolves only the zinc one, and that difference separates the two.