[irrational]

What does it matter whether they have blue pigment or not? If nearly every person looks at it with their own eyes and say, "That is definitely blue" then it is blue. I don't care why or how it is blue. Anything else is just pedantry.

[Green_man]

Some of the "blues" generated in nature rely on specific physical structure or other tricks to appear blue. This means they reflect predominantly blue light, but may not retain that "blueness" when ground/processed into a pigment. That's one reason there are few natural organic blue pigments, even the ancient Egyptians relied on chemical solutions for "Egyptian Blue".

https://en.wikipedia.org/wiki/Blue#Pigments_and_dyes

Interestingly, the one dye listed in the link above that came from a plant is indigo, which is extracted from the green leaves of the plant https://en.wikipedia.org/wiki/Indigofera_tinctoria . There's no animal or plant I know of that both appears blue and could be used to create even a poor blue pigment, though I'd definitely be interested in any exceptions I haven't heard of.

https://www.youtube.com/watch?v=3g246c6Bv58

[thangalin]

* https://www.sciencedirect.com/science/article/abs/pii/030504...

* https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5444072/

* https://www.jstage.jst.go.jp/article/fishsci1994/61/6/61_6_9... -- see figure 2 on page 4, showing extracted carotenoproteins

[Green_man]

Thanks, this is really interesting stuff!

[tipoftheiceberg]

When studying flora, things like color or inflorescence, for example, are examined with excessive concern with minor details, though.