The yellow stain comes from the nitrates. It was common among those who handled civilian dynamite, which contained nitroglycerine in diatomaceous earth.
The chemical burn will heal with no long-lasting effects, and the yellow will eventually fade and diappear. How long is hard to say, but it won't be forever.
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A chemical burn and yellowing of nails may take some time to heal. One thing that needs to be ruled out is inflammation of the lymph channels because of the chemical burn. This can also cause yellowing of nails. Treating lymphangitis can often treat the yellowing.
Please consult your PCP for primary examination.