Purple / violet / lilac.
I assume that this question comes in the context of a flame test.
Notice that all three ionic compounds given to you contain the potassium cation,
This should automatically tell you that if you were to perform a flame test using samples of these three ionic compounds, you would get the same color flame in all three cases.
More specifically, you would see a purple / violet / lilac color flame.
This color is specific to potassium cations and is characteristic of the emission spectrum for potassium metal. This emission spectrum represents the colors emitted when the electrons of an atom make a transition from a high energy state to a low energy state.