Try this site for good info on histograms.
http://epaperpress.com/psphoto/index.html
Histograms are more useful before final scan or before exposure(with camera) then after the event.
As someone mentioned - your eyes can tell you that you have it wrong. You don't need a histogram for that.
Histograms can be used to correct (by-the-numbers) not the best way, but helpful.
As someone elso also mentioned - there is no such thing as accurate or perfect colour, unless you are matching two samples.
There are people who see colour differently with each eye. Go Figure - It must give them some special problems.
PFitz