What is "Foveon Blue"?

D Cox wrote:

xpatUSA wrote:

SandyF wrote:

And what is the correct WB for a blue sky?

A Laurence-type answer, but in 2 words rather than one, [lol]

"It depends" or 3 words "Consider the illuminant"

I should asked a less terse question, sorry. If I point my cam directly at a clear blue sky and don't care about anything else in the scene, then what is the correct WB? It's a similar question to one I posted long ago elsewhere about watch luminous paint shot in the dark or a single traffic light in the dead of night. There were some quite varying opinions about that.

A semi-serious question but I used to those kind of watch pictures quite often and - me being me - I just had to ask. Not really a question for here, anyways - more for the technical cognoscenti, eh?

The technically correct white balance if there is nothing in the image but sky is for the sky to come out neutral grey.

An interesting statement. I see the logic, I think. It assumes that a custom WB was shot from a perfectly neutral target with a perfectly flat spectral reflectivity lit by the illuminant and the illuminant itself was shot with a perfect camera and perfectly processed.

So I'll clarify my question by example: suppose I wish to publish a clear blue sky with the hope that the reader will see the same blue as I did. What would be the correct WB then?

Or, if I'm selling a watch and the Buyer wants a shot of the glow from the luminous paint, e.g.

Image is from my post about the measurement of brightness here:

http://tcktek.blogspot.com/2011/06/exposing-lume.html

Since a Buyer would expect to see green 'lume', not gray, what WB would be correct for that? I mean theoretically correct, BTW, not 'close' or 'pleasing'.

[edit] I'm sitting here wondering if a custom WB were shot from a 'pure white' illuminant. Would that do it and where on earth is there such an illuminant? Illuminant 'E'? [/edit]