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  < unimpurpled >
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     \
      \

Part way through my second viewing of the article, I thought, "what is 'unimpurpled'". Wiktionary didn't know. Google doesn't return useful results for it, even. M-W, finally, clued me in: it's an obsolete term, with an "un" prefix, for the verb "empurple", which means to make purple[1].

[1] And a few similar things. https://en.wiktionary.org/wiki/empurple