>Blue is not
> beyond the range of the receptors in my retina,
I don't mean beyond the range of vision.
There are (so my ancient science tells me) three colour receptors, one in
the red region, one in the yellow, one in the green. These are stimulated
slightly by frequencies far off, more by frequencies close by, and sharply
by frequencies spot on. So perception of colour depends on the proportions
of stimulation between the three receptors. If red and yellow get
stimulated equally, and green only slightly, the frequency lies between red
and yellow; if red is stimulated lots, yellow less, green very little, then
the frequency is the other side of the red receptor. And so on.
So what I meant was, frequencies in the blue region are the other side of
the receptor - perception of blue therefore shades out into increasing
darkness, as the frequency moves further away.
As for lapis lazuli, and skies and such blue things, the Romans certainly
valued them - but how did they see them? Probably as we did - but my point
is that that is very hard to prove.
Peter