Quote Originally Posted by kbrede View Post
I have to plead ignorance here. What does taking a reference shot of a grey card do?
Thanks,
Having a "known" that is in the same light, in the same scene, allows you or your lab to match color balance to that reference point.

Doesn't have to be a grey card either. My favorite reference point is the dome on my incident meter but I've profiled my hand, several faces, ...

In my darkroom I use a Beseler PM2L. I program it (set the dials) to the known reference, say the dome, and adjust the enlarger filters to center up the needle for each dial and I'm ready to print.

The program is essentially the paper "profile", it does take some work to make the profile but once you have it it's easy as pie to set up. Insert the reference shot, use the PM2L to set the color head, insert the "real" negative, print.

This typically yields a workable proof with no color cast on the first try.