You can restore silvered photos with just a few clicks with color deconvolution. The attached image shows the original jpeg and the result of applying the color deconvolution plug-in
to it (after that I used hue/saturation to give the image a similar color range as the unaffected parts of the original). Note that this result suffers from information loss of the jpeg compression of the original and would be much better using the original scan. I only applied processes to the whole image, no selection / masks / brushes required.