Simple Color and Color Perception Question.

[BigDon]

I would have put this in Science, but more physicists post here.

The phenominom of yellow saturating into red. Is that physics or physiology?

[Hornblower]

I would have put this in Science, but more physicists post here.

The phenominom of yellow saturating into red. Is that physics or physiology?

I don't know what you mean by "yellow saturating into red." Can you elaborate?

[BigDon]

Yes.

A lot of yellow dyes in concentration appear red until you dilute them. Even works in reverse. Yellow solutions of dyes concentrating, then reddening suddenly at a certain threshold.

[StupendousMan]

Sounds like chemistry to me.

[kzb]

It might be the transition from transmitted light to reflected light?

[Ara Pacis]

Before barking up the wrong tree, I decided to use my google-fu.

It's physics and it's explained here. It depends on the dye, of course, but using FD&C food color dyes, from McCormick for the example on the page, you see that the yellow dye does not peak precisely and only in yellow, but includes red and some green. It seems to be more of a cut-filter effect than a more selective filter.

[Hornblower]

Suppose the dye in question has a very large attenuation factor in the blue range, a moderate amount in the green, and is almost perfectly transparent in the red. At low concentrations it will stop most of the blue light and let most of the green and red get through. That will create a yellowish tint. Increasing the concentration will stop more of the green light while continuing to transmit most of the red, thus making the tint increasingly red at high concentrations.