Maybe about 2-3 years ago I noticed a difference on my toe. The skincolor is darkening only on the upper left toe. I've tried using the pumice stone and it will help for a little bit and it comes right back. If I don't take care of it, it will feel a little rough but it's not as bad as a calus. It doesn't hurt or bother me. I've done some research but haven't found anything relating to this. Could it be a calus or possibly some kind of fungus? Is anyone familiar with this? Thanks.