So in the part of drop where oxygen is most plentiful (oxygen from the air is constantly colliding with the drop surface) the reduction of oxygen makes the solution basic.

Careful observation at the interface between the pink outer region and the inner blue region also reveals something about the corrosion process. Initially a cloudy white or very pale green area slowly develops between the two colored regions of the drop. Left undisturbed for some time this interface area gradually takes on a pale orange color.

Since the corrosion process is clearly electrochemical in nature it should seem logical that ion concentration will affect it. We see this most vividly in the HCl but that extensive corrosion is essentially an equilibrium effect since HCl will consume OH^- and "pull" the reaction forward. There is, however, a clear difference between the behavior of distilled water, tap water and sodium chloride solution. In that order they contain increasing concentrations of ions of various types.