Why are my gums darkening around a porcelain crown? (Photo)

You should go back to your dentist to have them check the gums. It is a possible reaction to the crown or maybe the silver filling in front of the crown.

Based on my experience, darkening around a porcelain crown is  more likely to be present whenever metal is used as a substructure for the crown ( PFM or porcelain fused to metal / gold crowns).   PFM crowns have an opaque “non-precious metal” , “semi-precious metal” or “high noble metal” alloy substructure that seals the tooth and offers  support for the tooth colored ceramic that is stacked on top.  Low gold content metal is a dark gray and is easily seen if not covered over.  Even 14 carat gold alloys have a gray color.  PFM crowns can be made beautifully by a skilled dentist-technician team but this type of crown is much harder to make attractive long term than all porcelain crowns or veneers.  Metal is used to give the crown strength.  PFM crowns are also used by dentists that have not been trained on the newer bonding procedures necessary for the all porcelain restorations.  Black areas at the gum-line can also be present if the border or margin of the crown is exposed and there is a difference in brightness between the restoration and the root.  All porcelain crowns made with high translucency material, do not have any metal and  can be the most aesthetically pleasing of all of the different types of dental crowns.

Sometimes you'll see changes in the gums due to a reaction to the material of the crown. It could be irritation of some sort. Are you having any pain or bleeding in the area? Definitely bring it up with your dentist.