Greg and Bill Schutt talk about horseshoe crabs on Ikonokast.

https://ikonokast.com/2021/10/27/episode-24-pump-a-natural-history-of-the-heart-part-1/

https://ikonokast.com/2021/11/10/episode-25-pump-a-natural-history-of-the-heart-part-2/

Mauve: How One Man Invented a Color That Changed the World

I’m equally certain that everyone posting here knows there are creatures whose blood is not red — the best known probably being the horseshoe crab.

This article in Vox gives a good overview of the various blood colors and their chemistries.

https://www.vox.com/xpress/2014/10/31/7133779/blood-blue-green-purple

Hat tip to WaPo for the doggies:
https://www.washingtonpost.com/news/wonk/wp/2015/02/27/12-fascinating-optical-illusions-show-how-color-can-trick-the-eye/?utm_term=.0fcf39cac1ee

They have some other examples there that are easy to verify by covering part of the image with a finger. (It’s just that I’m a sucker for critters.) Some of their images are of poor quality though.

There’s an xkcd one there that’s pretty good, which references the now famous dress.

This reminds of a book that i strongly recommend about the colour mauve and its history. It played a fair part in the development of modern industrial chemistry.
I think it was called Mauve, the colour that changed the world; or something similar. Really entertaining read it was.

And that dress. Don’t forget about the dress.

Pantone is a familiar way to go for printers’ spot colors. Munsell provides a more systematic and rigorous reference chart for generic science types who aren’t color specialists. Of the models used by designer types for describing colors numerically; RGB (for computer) and CMYK (for pigments) are common (but not used exclusively).

One caveat, color perception is strongly influnced by context. These dogs are colored the same:
http://brainden.com/images/yellow-blue-dogs-big.jpg

David, thanks for the comment. Great to have an expert on ancient colors such as yourself weigh in.

Interesting to consider the possibility that early color terms were for the process, which produced what we see today as a range of colors, rather than the actual color.

Also, as it widely but not accurately known, different cultures have different levels of intensity of naming colors. The Efe with whom I lived had white, black red, and green. Things that were lightish of any color where white, things that were darkish of any color were black, and certain things that were red or green were called, sometimes, red or green.

In other words, they were like me … not color blind but somewhat color indifferent. In a world where all things are natural (almost) color is usually not a useful attribute. Anything with a bright yellow, reddish, or orange color (meaning a warning of venom or toxin, like in a toad stool) are red to them. That’s all they need.

No Efe would ever say, “you know that one plant, with darker brown bark and light yellowish red leaves with the white stripes?” …. they would simply name the species. Using color to describe their environment is roughly like a car lover using color to describe model-make of cars.

(this might make a good blog post some day)

And yes, I know the smell of a rotten whelk.