No Blue Plants: The Bluebells Of The Rapture

Something I've seen crop up from time to time as I've tried to educate myself about my new home and the local plantlife is the idea that there are no "true" blue plants. There's this infrequent but recurring idea that cornflowers and forget-me-nots and nigella and bluebells are all lying to you and are secretly purple but using plant trickery to convince you of their blueness. Here's an Interflora blog which lists supposed offenders.