Acidic ferric chloride solution on treatment with excess of potassium ferrocyanide gives a Prussian blue coloured colloidal species. It is:

Step-by-step solution

If we add ferric chloride over potassium ferrocyanide, it forms a white precipitate that will become blue. The reaction is FeCl 3 + K 4 Fe ( CN ) 6 ⟶ KFe Fe ( CN ) 6 + 3 KCl Being small quantity of ferric chloride, not all potassium is displaced.