in poser 4 and later, ISTR  distance from front of camera to  focal plane
was 50 mm, but I can't recall how it were deduced.  human retinal cells ( rods or cones)
respond to luminance and wavelengths in some manner mediated by some part of  brain.
grey is white of low luminance and brown is dark red/orange.  "meaning of life" is to produce, thru
process of evolution, a sapient life-form that can create the higgs boson, at which point it
starts over again. also known as "big bang theory".

p.s. just to agree with ock's and WW's statements following this, interpretation of colour by human
brain is highly subjective and subject to trickery.  zappa was an highly innovative songwriter of
his day (OT).