I remember from school that photosensitive chemicals are kept in amber coloured bottles. Is KCl photosensitive? I read up the impurities list on the bottle and it says that it may have bromides too? So is it because of the KCl or the bromides? If it is due to the bromide, what sense does it make since it would react just to form another impurity?
On a sample of one selling site, amber bottles are cheaper than similar clear bottles, for some moderate to large quantities, at least today. KCl is fairly cheap so when selling the stuff in small quantity every penny saved counts towards profit. So: Economics could be the cause.
The potassium chloride solutions in my lab are in transparent glass bottles, as was the potassium chloride solution in my inorganic students’ lab at the LMU in Munich. If I recall it correctly, the solid potassium chloride we had there was in a transparent bottle, too, but don’t quote me on that.
There should be nothing in potassium chloride that will react under irradiation. And these types of impurities are generally not a reason to use such a bottle. But maybe the supplier of your choice just happens to have too many amber bottles?