If you read Dan Margulis' book "Professional Photoshop", he explains a lot
about reading CMYK/RGB values. Not all foliage, for example, is the same
green, but it varies more in luminance than in actual color variation. If
you compare known values to a picture that is "off", you can often see the
deficient color by examining the plate values.

I use a known flash temperature when shooting indoors. My camera "knows"
the color of that light and, coupled with it's AWB, manages to come
extremely close to "right on". Anything else is easily tweaked in Photoshop
if need be.

Wedding shots should be right, especially if the dress isn't pure white.
But then, only the bride and photographer would know that. Landscapes are
quite different because so many of them are "interpreted" rather than
"reproduced".

Mike Davis
mldavis2 AT sbcglobal DOT net
http://www.pbase.com/mldavis2/