Four hydroxide ions are bound to a zinc ion. Zinc hydroxide is amphoteric, dissolving in acid and in strong base alike, 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 2-, so the metal takes the -ate ending, and hydroxido names the ligand.
The solution is colorless. Zinc also dissolves in excess ammonia as the tetraamminezinc(II) ion, so the precipitate goes back into solution with either reagent. Aluminium does not dissolve in ammonia, and that is how the two are told apart.