Yes, darkening of decayed, demineralized sites occurs as the lesion arrests. This is similar to what is seen when caries arrests from changes in diet or increased use of other fluorides. A recent study showed that patients see the discoloration as a clear indication that the treatment is working. Similar to the treatment of eroded and hypersensitive dentin, the treated area can be restored using glass ionomer or with a sandwich restoration of both glass ionomer and composite. In lab studies, bond strength of composite by itself to treated surfaces is reduced but the clinical importance is unknown.  38% Advantage Arrest should not be diluted in an attempt to reduce discoloration. Studies have shown that diluted solutions may not be effective for caries arrest. Ionic silver adsorbs onto almost any protein surface and is especially tenaciously bound to denatured proteins. This accounts for the specificity to carious collagen over normal collagen, but both will stain. The differentiator between these stains is that with Advantage Arrest use, intrinsic pigmentation of a carious lesion occurs and surface protein staining occurs primarily on healthy tissue. These oxides are bound to the tissue and don’t wash or polish away. This is why the blackened lesion retains its dark color for so long, and is most likely the reason the antimicrobial effect is long lasting.  The functional indicator of effectiveness is when the silver oxide is bound to the diseased collagen. If the surface doesn’t turn black, the silver didn’t bind and the antimicrobial effect will only be short lived.