>And the Elves of Middle-earth almost certainly do not have green blood.
>AFAIK, Tolkien never states which colour their blood is, but that probably
>means that it is the same colour as human blood.

If this is seriously under question, see the following Elvish root:

YAR- 'blood': [..] Ilkorin _ôr_ 'blood', _arn_ 'red'; _Aros_ (Noldorin
_Iaros_) - name of river with reddish water

I rest my case.

>This is another case of me not remembering my sources :( but I was recently
>reading an argument that the order of the Berlin-Kay hierarchy probably
>shouldn't be traced to perceptual factors, but to material ones.   The
>argument went like this.  Languages which develop dedicated color terms are
>usually those whose speakers have items of manufacture distinguished
>primarily or solely by their colour; natural items tend to have other
>distinguishing features.  And, well, there just aren't a lot of good
>low-tech ways to make blue.  So blue comes late. 

I think there is a good support for that from the words for taste and smell:
We can manipulate taste worse than colour and have fewer words for the
corresponding sensations - 'bitter coffee' and 'bitter beer' really resemble
the green/blue merger, as the sensations described by the same word are very
different. We can manipulate smell even worse than taste and so the terms
are even fewer here - basically no at all, although there are some in
certain languages, as I learned from the conlangery podcast.
I have recently stumbled upon 'sweet' in Balto-Slavic (Lith. _saldus_, Russ.
_sladkij_) actually coming from PIE _*sal-_ 'salt', so that 'sweet' and
'salty' seem to have differentiated from 'spicy'. I would certainly like to
see an investigation of this in the same way Berlin and Kay did it for colours.

>Anyway, green is the colour our vision is most _sensitive_ to (aot
>"attractive"), so on perceptual grounds why shouldn't green have been
>Berlin-Kay colour #3?

But what does this mean in practice? If you have a red, green and blue lamp
of the same physical intensity, then the green lamp will appear brighter in
terms of perception. But for language, it's the synaesthetical qualities of
colours, like the warm-cool distinction which play a bigger role, I believe.

(Actually, in Tolkien's Elvish, green is seen as a bright colour - in
Sindarin _calen_ 'bright' even changes its meaning to 'green'.)

>Pure supposition here, but could a sensitivity to green (and its variations) be
>advantageous in detecting potential predators / prey hidden in undergrowth?

The peak of the sun's emission is at a wavelength of green (or
yellowish-green), I'm sure that's a reason for the sensitivity - but maybe
not the only one.