The reaction proceeds with the formation of a blue precipitate.

1) Reaction of copper (II) sulfate and sodium hydroxide to form sodium sulfate and copper (II) hydroxide:
CuSO4 + 2NaOH => Na2SO4 + Cu (OH) 2 ↓;
blue (blue) precipitate;

2) Reaction of iron (II) chloride and potassium hexacyanoferrate (III) with the formation of potassium chloride and iron (II) hexacyanoferrate (III):
3FeCl2 + 2K3 [Fe (CN) 6] => 6KCl + Fe3 [Fe (CN) 6] 2 ↓;
blue precipitate;

3) Reaction of iron (III) chloride and potassium hexacyanoferrate (II) to form potassium chloride and iron (III) hexacyanoferrate (II):
4FeCl3 + 3K4 [Fe (CN) 6] => 12KCl + Fe4 [Fe (CN) 6] 3 ↓;
blue precipitate.