To better understand the Mg galvanic corrosion, a gel electrolyte was employed. The gel electrolyte was doped with a pH indicator, serving to unveil and monitor the development of alkaline fronts that evolve in parallel with the evolution of H2. Using RGB (Red, Green, Blue) image processing as a semi-quantitative technique, it became feasible to generate transient 2D maps with proper detail regarding the pH evolution into the electrolyte and to provide new information about the galvanic corrosion of Mg. Findings revealed a significant pH decrease in regions where Mg dissolution was more pronounced. A local anodic polarization was achieved by coupling magnesium with A97075. The findings suggest that Mg hydrolysis is responsible for the local pH drop. Additionally, a biunivocal correspondence has been established between the maximum pH value observed in the electrolyte and the specific location where the Mg(OH)2 compound is generated.