The "white" magazine is cadmium plated. There is a difference of opinion about whether these date to the period in which your gun was manufactured or a bit later (around 1959). In any case, High Standard abandoned them pretty quickly. The plating process was flawed in that a corrosive contaminant was not entirely removed. When stored in less than ideal conditions, this can result in dulling external deposits forming but more insidiously the magazine's dimensions may swell. Such magazines left in a gun have been known to for all practical purposes become fused to the inside of the magazine well.
The cadmium plated High Standard magazines were the standard configuration from about 2/27/1954 which was the date of the revision F ( finish changed to cadmiun plate) for the magazine drawing until about 8/18/1959 which was the date of the revision H for the magazine drawing. The cadmium plating offered teh advantage of corrosion preventative and great lubricity. BUT, the factory did not always get a proper rinse of the plating solution that seeped between the inner and outer magazine shells. This allowed a residual metallic salt to remain behind and being a salt, was deliquescent and attracted moisture from the air which led to rusting between the shells. This rust pushed the shells apart resulting in various deformatives. The magazine might swell outward making it too wide to fit the magazine well. It might swell inward making it too narrow inside to load cartridges or both. There is currently no known fix.