Six cyanide ions are bound to an iron(III) ion. The oxidation state of the central iron is one higher, so the whole ion carries a charge of 3-. The potassium salt is potassium hexacyanidoferrate(III), also known as red prussiate of potash.
The coordination number is 6 and the geometry is octahedral. The shape is the same as the iron(II) complex; only the oxidation state of the central iron and the charge on the whole ion differ.
The solution is yellow. Adding iron(II) to it gives a deep blue precipitate, which is used as a test for iron(II). It was once called Turnbull blue and treated as a separate substance, but it is now known to be the same as Prussian blue.