[tipoftheiceberg]

Those plants that do appear blue are in fact often using a red pigment known as anthocyanin. Through pH shifts and a mixing of pigments, combined with the reflection of natural light, the plants are able to generate the appearance of a naturally occurring, blue color. That's the reason why plants such as bluebells, hydrangeas and morning glories appear various shades of blue, when in fact, as Lee explains, "There is no true blue pigment in plants."

[jacobolus]

> through [...] mixing of pigments, combined with the reflection of natural light, the plants are able to generate [...] blue color

We have a way to describe objects which “generate a blue color when light shines on them”. We say they are “blue” objects.

Likewise, bird feathers or butterfly wings which absorb/reflect light based on their small-scale structure and appear blue are still called “blue”, even though they might be colorless when pulverized.

There are plenty of “blue flowers” out there.

[tipoftheiceberg]

Right, but botanically speaking, we have not found a “true blue” plant.

[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.

[tipoftheiceberg]

Do you ever manipulate your hydrangeas’ color by changing soil pH? One easy way is adding used coffee grinds.