Britt, Although I've never experienced very dark to blackened boiled peanut shells, I've heard several explanations for this.
Aluminum pots. Aluminum pots blacken when boiling peanuts. Over time this darkening may transfer to the boiled peanuts.
Iodized salt. I've never experienced this myself, but some people say that iodized salt causes blackening of boiled peanuts. This may be hearsay.
Old peanuts. The inner color of peanut shells darkens from yellow, to orange, to brown, to black as the peanuts age. It may be that when this happens you have purchased more mature peanuts. Peanut harvest profile chart.
Apr 05, 2024
Disappointed in dark boiled peanuts by: Nora McDougall-Collins
Having been away from the south for 20+ years, I was looking forward to buying, eating and hauling home some boiled peanuts. But, the peanuts I bought at a stand in northern Georgia were dark and had a strong flavor to them. So, I had to throw them away.
Very disappointing.
Based on the reply, I will know not to buy them when they are dark.