yes agree with what law say.
No matter what potassium salt you are using, when dissolved in water, potassium ions will still be present. meaning if you are looking at the effect of potassium alone, doesn't matter if you use potassium iodide, potassium chloride, or any other potassium salt. KI is the chemical formula for potassium iodide and when dissolved in water, will give you K+ and I-, potassium ions and iodide anions.
If say use potassium (not potassium iodide), this means that you don't want iodide to be preesnt. coz either way you will still be getting potassium.
anyway, very interesting writeup and extremely useful.
green colour for SPS is from iron. Iron 2 ions are green.
Purple color for SPS is from potassium. potassium ions are purple in excited state.
i did not know the colour of the ions lead to the colour of the SPS. could be a coincidence though.