I can't see your photos clearly enough to tell, but....black soot is characteristic of rich mixture, oily black deposits can signify leaky rings. Is it also worn, as your thread title suggests, in addition to discolored? I can't tell.
Beyond that, you'll do well just Googling for photos to compare with your plug. Back in the pre-electronic era, auto mechanic instruction manuals used to feature these photos prominently, since changing out plugs (and points/rotors, plus adjusting dwell and engine timing) had to be done so frequently.
Hope that's helpful.
Mark
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