brown-purple color
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The oxidation potential of the halogens increases in the order I<Br<Cl<F, which means that if you have a solution of iodide ions and add bromine, the iodide will be oxidized to iodine, and the bromines reduced to bromides:
2 I(-) + Br2 → 2 Br(-) + I2
In the same way, two Br(-) will lose their electronsto a chlorine molecule, and the chlorides formed are going to lose their electrons if confronted with a fluorine molecule. This means that the opposite to the above reaction, i. e.
I2 + 2 Br(-) → no reaction
the brown-purple color of the iodine solution, when mixed with a colorless solution of bromide ions (from sodium bromide) will remain purple-brown, perhaps paler because of the dilution (a physical effect) which comes from mixing of two solutions but not because of any chemical reaction.
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