Do you ever wonder what are those dark specs in your peanut butter? If you are seeing these then I guess it is from your neighborhood startup manufacturer. They still have no enough budget to buy a good peanut grinder. Medium to top of the line grinders have the ability to pulverize well those brown peanut skins and mix to homogeneity. Yes, they are peanut skins. The brown thin covering next to thick shells.
Peanut butter makers have the option to choose between skinned peanut and the non-skinned version. Just like peanut vendors who offer wide variety of roasted and fried peanuts. The most common options are the ordinary and the “hubad” (skins removed). Some are choosing the latter type for health reasons. One manufacturer told me, the peanut skins can cause fluctuate of uric acid level leading to gout attack and possibly other urinary problems.
So, if you are concerned, choose peanut butters with no skins included!